This guide will how you how I build when I play Teemo. I will also tell you why I buy these items/pick the abilities, runes and masteries I use.
If you notice any mistakes or maybe if you know about an item I should add instead of one of the items I've chosen, just leave a comment.

This build will help you get a lot of both attack speed, damage and some ability power.
It will let you be fast enough and at the same time both slow and burn the enemy with your basic attacks.

The runes will give you everything you need for holding a lane. A option is to replace the Hp regeneration runes, with life steal runes.

These abilities works really good with Teemo, and every other champion. You can use the flash to catch up with enemies and to escape, if necessary.
You can, as another option use ghost instead of flash.