This guide is still under construction so pointing out some parts you might find interesting and helpful so i can add more to this guide would be nice XD.

Kennen is my favorite champion at the moment since he can fill so many roles in ranked ( top , mid , bot ) He can fill so many roles so why AP mid ? It is about how to influence the flow of the game. You can't only depend on winning your lane to win the game specially when you are in elo hell ( under 1400 ). This is a team game after all. Sure there are desperate situations but they rarely occur.

This build will be a balance of survivability and damage. I will prioritize damage early and mid game and more tankyness late game. You will be able to learn some tips and tricks of Kennen and for playing mid in general.

Feel free to leave constructive criticism about the guide on how I can make it better or what I should add. I rep+ helpful comments. Make sure to vote after you read the guide XD.
*Kennen art coming soon from my slowpoke friend*

MARKS

This is the most common mark for ap casters, no need to say much.

OPTIONAL

More and more Ahri players are starting to use these runes for more early game resistance. I find these not necessary on Kennen but still a viable choice.

SEALS

greater seal of vitality I really like the extra hp it gives since you can notice it right away from getting to level 6, it could save you from many heavy burst casters.

OPTIONAL

They can be very useful if you are trading a lot since they can reduce the damage you take from minion aggro.
greater seal of lucidity The little extra energy regen seems to be insignificant but when comes the mid/late game teamfight, you will often find yourself out of energy and unable to chase/escape with your E which almost cost half of your total energy(80).

GLYPHS

This is an other rune to help you survive high burst level 6 combo. It gives 24.3 magic resist at level 18 which is pretty nice since almost every champion in League of Legends have at less one skill which deals magic damage.

OPTIONAL

It has the same role as the glyph of shielding but it is better for pre level 6 trades. I take these instead of shielding normally for more early game domination so I can kill my enemy laner when comes level 6. Mobafire didn't have the icon for it.
You can take these if you like more damage but i find Kennen damage good enough.

QUINTESSENCES

Those runes add up with your utility mastery tree give you 9% spellvamp which is huge at every stage of the game. Having a Hextech Revolver is equal to having a Will of the Ancients

OPTIONAL

They are a good replacement since a few people have spellvamp runes. The extra 15 starting AP it gives is quite nice too.

CORE ITEMS


SITUATIONNAL
Buy this item when the enemy team has a fed AD carry or you are forced to be the initiator in teamfights.
Sometimes, this item is better than hourglass if the enemy has an aoe crowd control like Amumu's , Galio's or Leona's . You can use it to counter initiate which will give time for the first crowd control to wear off from your teammates. It can also help you with long crowd control like Warwick's or Ashe's
This is a good item if your team has a lot of magic damage and you dont' have to fear about getting heavily focus or crowd controlled.
Buy it only if you are forced to be the initiator. There is no need to buy it if you are far ahead since you won't be flashing in the entire enemy team until late game and you will probably have zhonya's hourglass and rylai's crystal scepter by then.
Get this item if the enemy team stacks magic resist, you will melt them. I don't usually get it due to its lack of defensive stat but if the enemy is using a slot to counter you, then you can use one to counter them XD

ITEM CHOICE
I take this item instead of boots first because Kennen don't need that early movement speed since he have his E. After only 5 minutes after you toke damage, the hp regen gives the same amount of hp as the pots (430 to 450).
The extra starting hp and armor will help you harass at early level without taking punishment. The extra hp is very useful when your enemy laner is level 6 and you get gancked.
This item has received some significant nerf on the cost and spellvamp. I normally finish it after i get rylai's crystal scepter or rabadon's deathcap. The hextech revolver with the runes and mastery gives 21% spellvamp which is enough for lane sustane.
I grab this after hextech revolver if my lane enemy is one of those massive nuker like Veigar or Leblanc .
I buy this after hextech revolver if I am not behind. The early you get it, you harder you will snowball but don't go in late game without rylai's crystal scepter.

R: This is why Kennen is feared for: his aoe stun which deals tons of damage. Max it first, not much to say.
W: Max this second if you are laning vs an enemy who is hard to harass and who pushes like a god then max this. You can use your W passive then active to deal some guaranteed. Your E-W combo can let you clear a casters minions line at a lower level. It might also help with skirmishes thanks to your R-W combo.
Q: Max this second if the enemy can zone you with long range aoe or locked crowd control. Its range will allow you to farm without getting in range of their crowd controls. You will also have an higher burst in 1 vs 1 lane kill situation. It is more than 50 extra damage since the AP ratio on your Q is 20% higher than your W.
E: I take one level on this at level 3 and max it last. While the extra armor and magic resist when activated is quite nice and the damage it deals on champions is actually higher than your W, the movement speed bonus does not change. This being your escape tool, you won't be able to get out of sticky situations if you used this to get in. Putting yourself at melee range is a huge risk so trying to deal damage with your E might result into a bad trade. You can take one point at level 2 if the enemy jungler have a good level 2 gank such as Shaco , Lee Sin or Alistar

These summoner spells are the most viable for AP Kennen. All the others summoner spells are useless for him unless he is playing an other role like AD bot but this guide is about AP mid.

This is pretty common on AP carries since it gives that little more damage which help them finish off people if their burst is not enough to do so. This is more for early game kill and late game, you will want to throw this on people with huge healing power like Mundo or Vladimir
It is an excellent initiation tool since you have an aoe stun. Flash is a nice escape tool which let you chase or escape. It is the most used summoner spell so nothing more to say.
Since you are pretty tanky after early game, you can afford to have this summoner which gives more mobility in a longer term. The extra movement speed is really useful in teamfight since after using your E and R, you are pretty much an AP carry in the middle of the teamfight and that extra mobility can help you chase better than flash would. This is the substitute of flash.
This is a nice summoner spell over all since you are not one of those heavy nuker who's role is to instakill a carry so you don't need ignite that much. A well timed teleport can save lives and even counter gank. It lets you split push and still be in an important teamfight in time. Having teleport in a lane also help you sustane better if you are having trouble.

ESTABLISH EARLY DOMINATION

The runes and masteries make you significantly tanky pre level 6. You can afford to trade a lot with your enemy but you normally won't get a kill until you get your ultimate. Start trading when you get to level 4 and try to bring him down low enough so you can kill him in one combo.

:This icon means you use your W's passive
Harrass/Gank from jungler: -> -> -> :Total damage:231 true damage
Lane kill: -> -> -> -> :Total damage:477 true damage unless the enemy have flat magic resist runes.
Ignite and auto attack to finish off.

The estimated damage is based on the fact that an AP mid didn't take the defensive tree and don't have magic resist runes. You can calculate your damage simply by looking at your opponent's stats. Knowing your limit can only be acquired through in game experience so don't worry.
If your flash is down or you don't want to use it, just use your W's passive after your W's active so you can still have the double stun. I always use flash when I know the enemy has an escape or a crowd control that can stop my initiation. I only started to flash when I played around 50 games with Kennen so don't force yourself. The confidence to commit will come by itself.

TIPS
-You can take enemy blue wraith when it spawns if all enemy members location are known. You will have to stand in the little corner just beside the brush so you can land your Q on the big wraith and have to small ones loop around avoiding some damage. It should be dead one auto attack after your second Q. You can use the experience advantage to get in some free harass when you have 2 skill and your enemy only has one.
-When being ganked, do not use your E right away. Find the best moment to use it so you can cover as much distance as possible. Your E can last 4 seconds,so getting crowd controlled before the end of its duration will be a waste. For example if Udyr comes to bear slap you, it is better to take the slap first, then escape without being slowed forever by red. Only let yourself get crowd controlled if you are sure the AP can't chain it, is too far to react in time, has no mana or don't have the damage to nuke you down.. This just might have saved your flash for an other day.

EASY:You can harass and come out on top if you do it properly. You will normaly be able to keep dominance over your lane and be free to roam and gank.
MEDIUM:They will either be able to out push you since Kennen early game farming is weak compared to other AP mid or have the potential to kill you with their burst. You can still dominate them in lane or at least keep it equal and not over extend.
HARD:They will be really tough opponent which are very mobile or have huge early game kill potential. They will also try to gank your teammates so call your MIAs. They are one of the reason why I take magic resist glyphs.

THE INITIATION
Teamfight is when Kennen realy shines. His ultimate is an excellent follow up to the tank initiation. You can be the initiator even if you don't have zhonya but you have to be far ahead because otherwise, they will just turn on you seeing they are not taking that much damage.
Champions that synergies well with Kennen is often the initiator of your team such as: Amumu Galio Wukong Malphite , pretty much every big range aoe crowd control that let you enter the team fight safely and to continue to chain crowd control the enemy team.

SKILL ROTATION
Before the really team fight, you should poke with your Q since its cool down is low and damage is high.
Don't try to get close for your W since they could initiate on you and get you insta killed. If your flash is not up, you can E in but you will lack mobility after your initial crowd control and burst.
After the initiation, your skill rotation should be: -> -> -> ->

It is very important to W right after your ultimate since it only takes one second to get in all 3 stricks. That means no one will be marked with by your passive. Right after you stun, E in their back line ( AP and AD carry ) and Q the weakest opponent. If you are not behind, you should be able to kill him or at less hurt him enough so he won't show up again in the team fight again.

I been playing Kennen for quite a while now and I decided that I had enough experience to make a guide for this fluffy squirrel.

Note that this guide is far from finish. I published it so my friends can see it and give me feedback on what i can do to improve it. If you guys have any idea on what i should add that is not in the list below, you can comment and constructive criticism is always welcome