This is generally the gear I use and the order I buy it in. It takes a little bit to get going, but once you get Hextech, kills start coming in alot faster..even more so after Rabadons. The only changes I would make to this build is exchanging void staff for lichbane, depending on the situation of the game ,and if you can get it or not.

If you think Teemo is supposed to be able to run into a fight and instantly rape everyone..well..you're doing it wrong. While Teemo can dish out amazing DPS, especially with this build, he has very low defense. I usually die a few times per match, but if played right, Teemo can absolutely destroy the other team with this build.

With around 450-ish AP, 2.0 Attack speed, and roughly 180-ish AD..Teemo's shrooms are a deadly tool when combined with his movement speed, blinding dart at the right moment, and his poison.

Teemo is best in a hit and run situation. Hit your enemey hard and fast. If they run away, chase them a bit with your runspeed, but don't get stupid. If they a melee chases you, turn around and lead them into a mushroom, then hit them with blinding dart and auto attack them to death in the 3 seconds you have before their auto attacks hit again.

If it's a mage that chases you..you have to be a little more cautious. Lead them into the shrooms..try to keep range. If they're squishy, you can usually kill them before they kill you. If they aren't squishy..keep range, hit them and run, and keep leading them into their mushrooms. Your best bet to kill them is to shoot them from behind as they run from your shrooms.