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 has been the build I have always used for Teemo, it has never let me down. With this build, you should have no trouble taking down even the most fed heroes. I focus very strongly in attack speed and armor penetration, although I have not attempted it with armor penetration runes. This will be something I look into doing when I purchase additional rune pages. The only thing you really need to watch out for are stuns, blinds, and really fed casters. If you have any comments, feel free to leave them here. Good luck!