This teemo build is the build i have used to ages, i have devised it and modified it to bring out maximum dps. I use this all the time and always win, enjoy! :)

Pros:
Good DoT
Great Farmer
Damage early game
Decent survivability
HELLA DAMAGE!
People with low health running into mushrooms and dying :D

Cons:
Squishy early game
Need to learn mushroom placement
Too fun.

I worked out that using runes for damage and attack speed was better than getting survival runes, as teemo is very squishy i used a slight damage build with defense which dramatically increases his survivability.

I chose these summoners spells as the fact teemo is a good chaser due to his W which makes him very fast, But as youre using auto attack you stop which allows them to move on further so thats why i those axhaust do you can fire a few more shots off and get the kill.

I also chose flash as it is a very universal spell as in the sence that you can chase and get away from focus at the same time. As late game you will notice the amount of damage you're taking. This is because the enemy team focus's you as your the biggest potential threat so they take you down first, this means you can get out of the fight quickly and recall.