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.
Speed Teemo, the speed demon!
This build focuses on Teemo's speed and ability to farm creeps. The builds for a late game 5v5 Teemo and not a very early gank driven one either. The team build up should have heroes good at 4 vs 5 fights, good teamates would be champions like Shen, Malzahar, Miss Fortune, and Tryndamere, or other fairly sturdy heroes.
Mastery Tree build: Since This build focuses on Teemo practically being able to be anywhere or get anywhere really fast you'll want to put points in Teleport and Haste, The rest of the build is a fairly standard DPS build for the masteries point. I didn't put any points into Quickness because 1) Teemo is a more offensive here, and 2) you really don't need it with this build.
Skill Sequence Order: Depending on how you play you can either put you first point into Blinding Dart or I usually put it Toxic Shot so I don't have to worry about mana. The rest should go to max out Move Quick as soon as possible. Once you hit level 6 you'll wanna get your mushroom bombs and start planting them all over the map. Make sure to keep them by Baron and the dragon. The rest of your abilities can go into Toxic Shot and Blinding Dart, I usually max out Toxic Shot first so I have more mana for mushrooms and save the darts for last.
Rune Builds: Remembering that Teemo is an assassin I went with damage at level 18 for the marks, movements speed increase quintessence (yah I know, theres that whole speed thing again), crit damage for the seals, and crit chance for the glyphs. I find that a crit and damage focus plays better to Teemo than AP and attack speed. towards the end of the game with this build you'll be able to solo Nashor and get to anywhere on the map in a couple seconds.
Purchase Order: The first item I get is Boots of Speed to build to Boots of Mobility and two health potion. After that I build towards getting Zeal to build towards Phantom Dancer; I get two Phantom Dancers before getting damage items for the +30% movements speed increase. With the Phantom Dancers plus the Boots of Mobility and his passive speed boost in combination with Ghost and Teleport you'll be able to get from opposite ends of the map in seconds. Now for the damage items I find attack damage to be more useful for killing than ability power so I will go for Infinity Edge for the extra crit damage, since with it you will have like +80% crit chance just with your items. And then I either go Bloodthirst or The Black Cleaver for armor reduction and a good amount of AD. Now I know you're probably thinking that these items are super expensive but you'll be able to farm creeps like nobodies business; as soon a big group of creeps starts pushing one of your towers just run over there and drop a mushroom right in the middle of them.
Notes on how to play: One of Teemo's most useful abilities is his ultimate Noxious Trap; you can have an unlimited amount of them out at a time, they're great for killing a large groups of creeps, they slow when triggered, and they give sight where ever they are. Those little mushrooms act as virtually an unlimited supply of wards. If any of you remember "Map Hacks" for Warcraft 3 while playing DoTA, its biggest benefit was being able to see the whole map. With the proper placement and usage of your mushrooms you can have visibility almost everywhere. Starting a game, like I said earlier, I usually start out with Toxic Shot and do a hit and run attack. For example, when laning against champions like Mundo or Ashe, stay behind your creeps and pop out when they get close enough to hit. It will be easy to hit them since the first of boots will make you fast enough to hit and get back behind your creeps so you can dodge Mundo's cleaver or Ashe's Volley. I know your not going to be able to escape all of the attacks but thats why I start with 2 health potions. At level 6, when you get your mushrooms start planting your mushrooms in bushes, by dragon, Nashor, and at good intersection points, this will help prevent ganks, as long as you keep an eye on the mini map. If I haven't already, at level 7 or 8 I put a point into blinding dart for the attack miss effect, its great for taking less damge from jungle creeps and helping a teamate who is getting hit by a melee heavy hereo, like Master Yi. After that I just run aroung planting mushrooms, farming creeps and help out in team attacks as much as possible. I hope you find this strategy fun and useful when playing Teemo.