Hello Summoners and welcome to my Kennen's guide! I am a Gold 2 player, but I don't rank a lot (70 rank games/ season). Even though I usually Mid, I will start playing top more often to add tips against Top champions. I'm actually testing a Kennen support build, if it works I will add it to this guide. (Kennen has a good potential with Kalista)

Kennen is a mid/late game champion. This is why I take Greater Glyph of Ability Power to get a better early game. If you plan playing passive (e.g. Against a big counter, such as LeBlanc ), go for Greater Glyph of Scaling Ability Power.

Once your combo is done and your target's almost dead, Kennen has nothing to secure the kill. This is why I take Ignite. Well it's not complicated, Ignite is never a bad choice.

Flash is a must with Kennen. Even though you have your E to escape, you become ungankable with Flash. In teamfight, it allows you to E, Flash in and ult.

I usually start with Boots and 4 Health Potion. It allows you to dodge most of mages skillshots.
It is possible to start with Doran's Shield while laning Top for more sustain/resists.

If I lane against AD champions, I'll start with Cloth Armor and 5 Health Potion to get Seeker's Armguard when I back.

Seeker's Armguard is great against every AD mid laners and it is a part of your Zhonya's Hourglass.

Hextech Revolver is great against aggressive mid laners, it gives you sustain and damage to fight back.

Zhonya's Hourglass is ALWAYS your first item. It allows you to go all-in and ult without fear to give a big CC advantage to your team. It's great to have it early, since it can win crucial fights like Dragon Fights or Ganks Bot lane.

Sorcerer's Shoes is always is a good choice, since you only get Armor Pen with your last item.

Ionian Boots of Lucidity are good too. It depends on your playstyle. CD is good, but I really suggest Sorcerer's Shoes.

I like to upgrade to homeguard early game, because this passive combined with your W allows to go back in lane really fast. So you don't miss many minions and the enemy can't push your tower easily.

Rabadon's Deathcap I go for this item right after Zhonya's Hourglass. It gives you a strong mid game with over 400 AP.

Will of the Ancients is a really great sustain for Kennen. Your Q has a low cooldown, so you can easily farm and heal with it.

Rylai's Crystal Scepter is a late game item. Even though you got your Zhonya's Hourglass to save you, your enemies get stronger and can one shot you before you could go back after your ult. Rylai's Crystal Scepter will slow them to allow you to escape or chase them and you get around 2400 health with this.

Abyssal Mask balances your build, you got armor with Zhonya's Hourglass, you got health with Rylai's Crystal Scepter. Now, you get magic resist and even more damage. Its passive works well with Kennen, because you're usually in the middle of a fight. It is usually my last item.

Void Staff is an item to consider. I rarely buy it, unless the enemy team built full magic resist.

Mark of the Storm is a great passive that allows you to stun your opponent as much as you want. In a 1v1 fight, you will usually stun your oppponent twice. It's good to escape since you can Q your enemy while you run and finally stun him to escape him.

Thundering Shuriken makes a lot of damage. I use it to harrass the enemy all game long. It's great for farming. Its low cooldown allows you to do it a lot.

Electrical Surge is awesome to harrass short range champions. Every 4th AA. you get a free Mark of the Storm on your next AA. Use it to harrass your opponent. If he satys back when he sees your 4th AA, use it to deny him in lane. Don't AA minions, farm with Thundering Shuriken so he will lose farm. When you do farm with your 4th AA, quickly AA minions to get back your mark and bully the ennemy.

Slicing Maelstrom is a free stun. It's really good in teamfight, has a lot of damage, stun the entire ennemy team and often have a "panic" effect in the other team and they get disorganized. Don't be affraid to use it in 1v1 (Only early/mi game), it will do a tons of damage really quick and will give you the kill. Late game, NEVER use it for a single target. Keep it for a teamfight, don't waste it when you know you are going to die and your team ir too far. Late game, the way you use your ult will often determine who wins the game.

Pros

Great CC.
High damage.
Great escape.
Do amazing to follow jungler's gank.
He's old, but rarely played. Most of the time people don't know how to deal with him.

Cons

Short Range.
His ult can be deny with a knock-back. (e.g. Tristana, Alistar, Lee Sin).
No minion wave clear.

You don't realy need jungler ganks, since you can easily play safe and never get killed against a counter champion or just bully your oppponent. However your jungler will love ganking mid, since Kennen goes well in ganks. Prepare your 4th AA, before engage and follow with E-W-Q-AA-Q.

Follow your mid whenever he tries to gank, your presence in a balanced fight will give the advantage to your team. Your ult will win the fight and allow your teammates to get some kills.

In mid/late game teamfights, never be the one to engage. You need a real engage, so you can follow right after. Otherwise, you will get killed before you can even be in position and ult properly.

A lot of Kennen start with Doran's Blade, but you should not need it. Your AA animation is fast enough to kill a minion with your base ad. The low cooldown on your Thundering Shuriken helps you to farm and secure the big minion.

Try to harrass your opponent with Thundering Shuriken. When it hits its target, follow with Electrical Surge. If your opponent is good at dodging skills or stay behind minions, use your 4th AA and follow with Electrical Surge. Whenever you have your 4th AA ready, keep it a little bit, farm with Thundering Shuriken to avoid to use your AA. If your opponent stay back, don't lose farm for harrassing, just keep farming and get another 4th AA ready to surprise him and keep him away from his minions.

Once you hit level 6, keep harrassing your opponent. When he's halved, get your 4th AA ready, engage with E-R-W-Q-AA-Q, finish with Ignite if necessary.

When you lane against your counters, play safe, farm with Thundering Shuriken to have a longer range. Last hit minion with AA when you can. Farm undertower : To farm mage minions, I usually AA-Tower shot-AA. To farm melee minions, simply wait 2 Tower shots and AA. NEVER get killed. Ganks can help you, but sometimes it's just hopeless (e.g. Leblanc), hold your lane and tell your jungler to give advantage to other lanes.