Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
This is a Teemo build that focus on high attack speed and cooldown reduction in the early to mid game. The later game focus on items that increase attack damage and health to make sure that Teemo survice thiose pesky tanks.
The item builds allow for variations that enable your Teemo to withstand a wide variety of opponents.
The first item you should go for is Dorans Shield and a Health potion. This will enable you to stay in lane long enough for you to gather the gold necessary to buy Mercury Treads.
After that you should go for Nashor's Tooth to increase your attack speed in the early to mid game. Health Items, cooldown reduction and Ability Power items has been selected for the late game to be able to withstand a measure of beating as well as start to deal a lot of damage fast.
The ability leveling scheme has been designed to focus on leveling up your autodamage ability as fast as possible (Toxic Dart). Alternate between Toxic Dart and Blinding Dart during yoiur first couple of levels. Depending on your opponents and their range you might want to level up Move Quick earlier than what I propose, but the idea with this build is to increase your damage, attack speed and cooldown reduction as fast as possible. Mercury Treads should keep you fast enough for up to level 6 or 7. If you encounter an opponent with a very long range however you might need to bump Move Quick to level 3 or 4.
Runes should be selected that grant you health and attack speed. This will help you in the early game. I just selected a few examples in this build. The particulars are up to you. I find that I most often have runes that give me 15% attack speed increase.