Hello, i am a plat league player on EUW, my ingame name is Zefiion. I swear my intentions are only to help the starters off, and with this guide it will help you hit 30 or high elo in no time!

Magic pen cause you deal mainly magic damage
Armor cause u will nearly allways match alot of physical damage (junglers deal ****loads of damage early u know)
Magic resist because if you are up vs a magic damage enemy without magic resist, u gonna have a bad time!
Mspeed cus it helps you escape, and makes you even more of a sneaky little ****! More utility in general!

These items provide you excactly what you need, it gives you just enough tankyness, enough damage, and one crazy *** movespeed! This is the best possible way to splitpush with teemo, and annoy the **** outa ur enemies! If you doubt my build works, try it, i guarantee u lots of fun and most likely lots of progress!

Standard setup for teemo, we're not going ap nuke teemo thus we max E for the poke/harass

Allways go flash and ghost, this makes you extremely hard to catch off guard late and early game in addition with the itemization u will be splitpushing without worrying bout getting ganked ever!

Offense is self explained, it makes your damage stay high even tho you will be building mainly defensive items. The utility is for mana regen in lane and movespeed to get faster to lane/objectives/run away.

Pros: Tankier than full ap teemo, you will not rely on shrooms to do damage.
Hard to get caught.
Annoys the **** outa enemies.
Strong in lane.
Wrecks turrets/inhibitors/nexus.
Fun to play!

Cons: Will be hard to master for newer players.
Weak untill you get shurelia and twin shadows.

Shrooms everywhere!
More seriously tho, you will draw the enemies attention to you while you are splitpushing, enabling your team to go for other objectives. This might sound bad, getting ganked and all constantly, but what does it matter, with this build you wont die even how hard they try to catch you.
TL;DR
Help your team by shrooming objectives and releaving pressure of your team by drawing enemies to you.

Push push push and go for turrets!

Thats it for me folks, believe me or not, this stuff is gold! Have fun, spam your laugh, and last but not least! piss of your enemies! :D

Side note! Check out my friends darius guide, he is a diamond league top laner, and darius is hes main! http://www.mobafire.com/league-of-legends/build/diamond-league-to-dunkmaster-darius-296703