Hi summoners, i'm Masni and this is my first build on Mobafire, so, let's get start..
I'm gonna tell you, how i'm playing for AP Teemo, by the way, i think he's better than AD. So it's not so pro build/guide, anyway i hope it'll help you enough to get best score of the game.
I will tell you, how to Farming, Whereto place your mushrooms(in early & late game), to get kills, if the enemy escape from teamfight and going through jungle to safe yourself.

Pros :
Caster - winner in 1v1(by blind)
Killer with mushrooms
Disappearing from teamfight very quickly(W + R)
With full EQ it can waste its mana

Cons :
Often focused first
Low hp - no survivability
On mid isn't enough good..

If is the huge wave of enemy's minions, and you got your ultimate on 2 level + over 200 magic damage(by ability power), you can place the mushroom between melee minions and the magicians.
It's strong enough to get more than 8 farm, if you shoot with your basic + passive from E, you can kill the cart too..
At the beggining of the game, you shouldn't wait on last hits, your poison could kill the magician minions, but you don't need have so big farm, from 11 level, you will have big(R'll do everything), anyway, it wont mind if you will farm as you want.