Sup, Venomous here bringing you an awesome new build.
Teemo AP. My favorite way to play him, its just so dominating.
Outplay solotop, anti gank mushrooms, great dps output.

The runes are pretty much Ability power, some mana sustain and some magic pen. Its needed early game.

As masteries i took 21 - 9 - 0 since i'm going agressive ap and pokes will make the difference.

As spells i prefer flash to get away from dangerous situation and ignite to secure my kill.
Heal or exhaust are a change for ignite, Thats the only usefull's i can see right now.

Now this is where everything gets fun.
Your pokes will make your team go insane because mostly you'll take all the kills because of the poison. Gotta love it right?

Teemo's toxic shot is your main damage, its dps so poke once in a while. You will force them out of lane sooner or later. Take advantage of this.
Is there an annoying ad carry or tryndamere, blinding dart will blind them making you immune to basic attacks for a couple of seconds. Another advantage.

Early game farming will be necessary. When you get your first item the fun begins. Do not play too agressive without it. Have fun.

Very great solotop; You see that mushroom? Thats not a mushroom. Its an anti-gank device!
Great early game sustain.