This is my first guide. send me tips and such.
Teemo is a very fun champion to play, but he is hard to master.
He is one of the fastest champions, if not the fastest due to his skillmove quick.

Starting with build #1 the AP build.
I get Magic pen for my marks(red) best way to go. period.

I get the attack speed seals (yellow) reason, I build attack speed to get as many hits off as possible.Teemo's toxic shot does extra magic damage each attack, based off your AP so getting as many hits off as possible is key, also if they run you want your hit off last so you can get the kill if they are low.

I get AP for glyph, .99x9 = ~9 extra AP. The blue glyphs for AP are the highest about per rune. best bet for and AP build on any champion.

My quintessence
Get AP or Magic pen, based on your preference. I like the AP ones.

NOW FOR BUILD #2 AD/AS
For my red runes get Armor pen. This will help your attacks break through all those tanks with high armor and be a tank killer.

For my yellow seals, critical damage. These runes are very expensive(810 each) but they are VERY powerful. You will have a high crit rate/attack rate, so crits will pop up A LOT, especially after you get your phantom and infinity.

My blue glyphs I get crit chance. This build is very critical heavy. You will have a VERY high a speed if not maxed very close, plus your damage will be high and crits will be very common.

Quintessences are your choice, based on how you prefer.
Pick crit chance, crit damage, or attack speed, however you feel or do one of each, however you want.

AP mastery build.

Mental force <4>
Sorcery <4>
Arcane Knowledge <1>
Havoc <3>
Blast <4>
Archmage <4>
Executioner <1>
Then move to Utility.
Expanded mind <3>
Good hands <1>
Scout <1>
Meditation <3>
Good hands <1>

Boom! your set.


Now for Build 2.

Summoner's wraith <1>
Brute Force <3>
Alacrity <4>
Weapon Expertise <1>
Havoc <3>
Deadliness <4>
Lethality <1>
Sunder <3>
Executioner <1>
Archmage <4>
Now move to Utility.
Expanded mind <3>
Good hands <1>
Scout <1>

Skill prioties are the same for both.
Your is your just awesome. It's a ward, Nuke, slow, DoT, and just awesome. Put them in brush, on edges of them, also if you notice a spot that they enemies are going to a lot, put them there and see if they still go there for long. Your teammates may also ask you to put a few in areas, listen to them. They will love you for it.

Next your toxic shot. This skill is also very awesome. It will poison your enemies and do bonus damage on each hit. This is why you want the extra attack speed, it makes your basic attacks hit very hard. This skill is much strong using my AP build, which is what I recommend, and What I myself use.

Then your blinding dart. This skill has a larger range than your basic attacks, so it can be used to kill from afar. Focus using this skill on the AD carries, it blinds them for a short period, making all their basic attacks miss. For example if your figting Master Yi, use it after he uses his skill highlander, making it miss. In earily game, I use this to harrass, I hit them with a basic attack then with blinding dart, then a second basic attack for a total of 3 quick hits and a poison, and if need be a move quick to avoid getting hit. It can be a strong nuke with enough AP.

Last but not least Move quick. This skill makes Teemo very mobile. It has a passive making him fast, but any hit from a champion will cancel the passive for a few seconds. It also has an active cast, making Teemo gain double his movement bonus, and this is NOT canceled from champion hits, It lasts for 3 seconds.

Your passive is helpful. Camouflage. This makes you become stealth after 2 seconds of not moving, attacking, or using a skill. This can be used for many purposes such as:
1. Getting an advantage to gank enemies. You remain stalthed until the opponent passes you, sandwiching them between you and your team. You gain an attack speed bonus after becoming unstealthed for a few seconds.
2. Hiding from enimies, If your low on hp and getting chased you can use move quick to run away and then find a safe spot, sit still and wait 2 seconds and become camouflaged.

Pros:
Very good damage output with either build.
Fun to play.
Team loves you.
Set out many little wards
Unique
Good at midding.
Very fast and mobile

Cons.
The biggest con. SQUISHY! Teemo is extremely squishy.
Can be hard to master.
Team may get mad at you if your poisons kill steal them.
He is a big (yet little) target, due to his low HP, and high damage.

Despite his squishiness, He can be effective in the jungle. You want to get the red buff form the lizard, stacking the dot from that and your poison, this will be a nice damage increases. The blue buff will help, but not as much. He is also good at soloing the dragon later on. Hit them with yourand then just attack them. They will die fast. You can also put down your http://edge4.mobafire.com/images/ability/teemo-noxious-trap.png mushrooms and lure them in for some extra damage. Taking baron is quick with Teemo in the back, and when you do make sure to cover anywhere the enemies could come gank you with yourmushrooms.

Hiding the the jungle to pick off weak fleeing enemies is easy, just go to a common brush, camouflage and then boom pop up after they hit recall and happy Teemo, they die.