When you pick Teemo, you are probably going to be carry at bot or AP at mid. Forget those plans, and head to top and build yourself as a tanky DPS and feel like a man, while playing Teemo. Tanky DPS Teemo has great early game adventage against all physical based champions who dare to step on your lane, and due to his built-in ward ability, the junglers won't have any chances to lay a finger on you, ever. Tanky DPS Teemo can soak damage in midgame and early endgame like a true tank, and still keep himself in shape of other damage dealers.

Passive - Camouflage
Your passive makes you a living ward, if you stand 3 seconds still. It can be used in early game ambushes, and an experienced Teemo player can position himself for upcoming teamfight in a spot which gives the element of surprise. When you exit your camouflage by moving, you should use your attack speed booster it gives to harass enemies or do as much effect you can with it.

Q - Blinding Dart
Your Q is your only Hard CC, so don't waste it. You can turn 1v1 fights to your victories, when your enemy is totally helpless against you for the decisive amount of time. Later on try to interrupt opponent's carries with it to prevent as much damage income to your team as you can. Take it at level 2 and max it by level 13, because you'll need the longer duration only at midgame and later on.

W - Move Quick
This ability will save your furry butt many times. When escaping or initiating, try to avoid any unnecessary small damage income to keep the passive movement speed bonus on. This proves that Sunfire Cape isn't very useful on Teemo. The Active part has good uptime, and you should use it to harass, initiate, escape, move quicker from base to fight... basically anything that gets boost from mobility. Take this at level 4 and max it by level 18.

E - Toxic Shot
This is your earlygame's most important skill. Your auto attacks deal even more damage over time, which makes Teemo an excellent harasser. It makes lasthitting easier and auto-attacking enemies can prove really useful in laning phase. When an enemy approaches, you have a plenty of time to shoot a couple of Toxic Shots upon your enemy, and before he realizes, he's in deep doo-doo. Take this at level 1 and max it first.

R - Noxious Trap
This is what makes Teemo annoying to play against. In earlygame, keep the river secure from gankers. Keep your top bushes enlightened. The best of all, slow your enemies and deal devastating magic damage over time on them. If you get in melee with opponent champion, always try to position a mushroom under him. Mushroom's damage over time is really High, and if your enemy decides to retreat, you won't let him get away. With your Auto-attacks, Q and E, Mushrooms will prove to be very deadly in fights. In teamfights, place mushrooms under as many players as possible to maximize the damage, or put them on potential escape routes. In either way, the slow and the damage will prove really useful to your team.

Start with boots and health potions. It gives you mobility, which is the most useful stat for Teemo in the early game. If you're heading against 1v2 lane, you can still keep your sustainability by playing safer and buying Regrowth Pendant, which you can upgrade to Philosopher's stone, if necessary.

When the laning phase goes on, you should boost your sustainability like a true tanky DPS with Wriggle's Lantern and Mercury's Treads, to keep yourself in your opponent's level in damage mitigation. In late early game, build some midgame items, like Phage and Hexdrinker to increase your harass and mitigation potential even more.

At midgame, start finishing some items. Frozen mallet is an absolute boss choice for Teemo, due to his mobility and crowd control. Maw of Malmortimus and Atma's impaler are both good items to devastate your enemies in small teamfights. Enemies have more reason to focus you, and you still can be the boss, tanking a lot of damage without dying.

Finish your build with Madred's bloodrazor, which is a great endgame improvement to your E's Passive effect. Sell Wriggle's Lantern and buy Banshee's Veil on it's place to boost your defensive and offensive stats even more, and you can soak even more cc in if necessary.