This is my first attempt at a guide so be as nasty as you want but leave reasons and tips when you hate :) .

So basically teemo has been an easy champ to use but i was clueless for a while on his build so i read into other peoples guides to get different builds, so the build will be similar to other peoples. However i will be explaining the details about teemo in this guide also.

so basically teemo has a nice passive poison and he uses basic attack alot, so i have him built as a hybrid, however mostly ad. the ad and ap per level runes help teemo scale his damage while he farms for the items, and the solid ad runes help him for burst in fights for a fb.

P.S. dont question my utility masteries. The xp bonus is needed so you can hit level 6 as fast as possible. ITS ALL ABOUT THE SHROOMS!. The bonus 1 gold per second helps if you find it hard to farm (look at my final comments - bottom of page)

PRO's:

Good Damage Output
Fast
Fair Farm/Harrass On Lane
Good Gank And Survival Ability

CON's:

Stuns, Slows, Fears Etc... Will Screw You

Focuses On Damage; not much mr

Will Get Focused Alot

Your Team Will Hate On You If You Dont Shroom Often Enough (and we all hater haters, lol)

So Basically teemo has his basic attacks to make damage output like i said earlier, he needs the ad to make constant damage so we start with a dorans blade, this will help give teemo better damage he should have 60-70 ad, with that small boost from the poison, this will make him very good for level 1-5 harrassing.

The reasoning for the pots after the boots is, unless your game is going perfectly the enemy should be hitting you once ever now and again and the pots basically keep you on lane.

The laning phase is the best time to farm... you must learn to farm if you are going to use this build.

However if you get a Kog'maw or a caster that can compeltely out-range you, your harrass is going to be pretty pointless, if your mid ( i dont mid with teemo much tbh) you should stay safe and last hit minions as often as you can, and at level 6 place shrooms where the enemy often stands to attack you.

If your early laning phase is on bot/top lane you have unlimited harrassing capabilities, teemo can use a brush for cover from basic attacks from dps carries and spells that have to be focused on a single champion. USE THIS TO YOUR ADVANTAGE! stick to the middle of your lane with your partner and harrass them; this is how... firstly take a brush, yours preferably since its safer, now you have to run out your brush slightly and hit one fo their champs thats in range, then run back in your brush. NINJA, they cant hit you without face checking and being wreckless. They will however ward the brush eventually, by this time you should be level 6, which means you can place your shrooms in the brush, and down the edges of the lane where the enemy should be walking.

TIP: DONT FORGET AT LEVEL 6 YOU CAN USE SHROOMS AS FREE WARDS. ITS A MUST!

Ok so teemo is farming nicely (I HOPE), this should mean you've finished the Berserker Greaves and started to build the Malady, or your ahead and thats even better.

Mid game focuses on ganking quite often, sometimes its from the enemy team, so you need to continuously place your shrooms, shroom the dragon, shroom your lane enterance, and if you want to be helpful shroom the side bushes on mid.

Now you should have shrooms around your lane and possibly around mid and the river, when theres no enemies, and the opposing mid champ is over stretched, you OR a teammate can make a safe path up to the mid bush. If its another champ go to a guide for their ganking information. If you are ganking, then you want to bush camp a bit, dont worry if an enemy pops up in the brush, you should be invisible from your passive.

Once your set up get your ally to initiate and you cut the enemy up from behind them, if its an ad carry on mid use the blinding dart ability, it helps alot, if it isnt auto attack them to death, its 2v1 you should win. Shrooms you placed earlier will show you any enemy champs coming to counter your gank.

If you are in a dangerous situation use your move quick ability to out run them, you should out run most champs, however if its a champ like gangplank with his insane speed... your going to have to hide with your passive somehow (BE CREATIVE, DONT DO THE OBVIOUS)if your invisible only his ult can target you or you will have to flash while you have move quick activated this should give you enough distance to reach a turret.

TIP: KNOW THE ENEMY, invisibilty works 75% of the time if their abilitys have to be focused onto the enemy champ.

TIP 2: Oracle Can Be Effective On Teemo If They Are Using Vision Wards. Eliminate The Ward So Your Safer!!

So after that nice long mid game you should be moderately wealthy in monies. by this time you should have your Frozen Mallet and moved onto the Madred's Bloodrazor. By now your game should be one sided. If your unlucky the enemy will have fed off some feeder on your team. Or your playing a balanced/good game and should be getting pleanty of team fights.

In the team fights, you want to linger behind your team until you or the enemy have initiated. Hopefully this means theres less chance of them focusing you, if they are focusing you run around with your W skill, hopefully the opponents will chase you until they think youve gone.

THEY WILL TURN AND ATTACK THE REST OF YOUR TEAM! this means your open to return and take out their team. DO NOT FORGET TO USE BLINDING DART ON THEIR DPS CARRY! the amount of teemo's i've seen fail because of that one skill not being used is worrying. Basically in team fights you and your team should be focusing their damage output champs... it's kind of obvious.

By now a team should've won... OR its a long game and you still have an item or two to get. I suggested for the build a Bloodthirster its a 100 dmg item if you get it farmed with minions/kills/assists, and it gives you a fair bit of lifesteal too. However this can be swapped for other situational items:

Phantom Dancer - this is useful if they have fast champs, e.g. gangplank/xin zhao... this should make your speed enough to keep them away with your passive
Banshee's vail - useful if theres a karthus ult killing you, or if their casters focus you
Zhonya's hourglass - optional choice from banshees vail, it offers you buffs on your poison, extra armour, and when activated will negate karth ults.
Rambudan's Deathcap - a choice if you want more DOT from your poison etc..
Guardians angel - mr and armour, increases survivability alot with its unique passive.

One of these should be your 6th item after you've sold the dorans blade.

TIP: SHROOM BARON! SERIOUSLY BARON CAN CHANGE THE TIDE OF ANY GAME!!

TIP 2: Watch Your Minion's Movements, You Will See Where Enemy Minions Will Move If They Are Pushing, Use This To Your Advantage Place Shrooms Where Their Minions Will Be Walking If The Enemy Pushes!

Anti-push shrooms can be the best defence if the enemy scores an ace, it forces one of their champs to tank turrets and often stops them making a complete push for victory.

Also I repeat: shroom the lane edges, the enemy often walks there.

Teemo is a heavy damage champ with full items. He is capable of taking out tanks and surviving most fights.

He is most usful midgame when he is shrooming around dragon, the river, and the lane edges.

I play teemo alot, i revently played a game against an alistair and jax... it was pretty much hell for me... their sequence of headbut and pulverise directly after (resulting in me being thrown where i was originally) and jax following up with his empower ability and leap strike. This was effectively killing 60-70% of my hp so i found it really hard to farm on bot lane, however i did get a bit of gold passively and got a few ganks off... we lost that game in the end; other lanes fed -.- GG.

Anyway, teemo is a very squishy champ; he is very versatile and heavily team reliant late game.

Hope This helps somehow :).