hey guys, first of all, my english is not the best, im portuguese and i will show my build for that little guy Teemo.
I always play sup, and sometimes when i see my team dont have a real carry i pick Teemo for support. i know isn't like a real support and teemo get some KS because of poison, but, he can ward all the possible ganks and let their jungler take to much damage to try the gank, and save ADC. but the best of playing teemo sup is when your team take care of team fights and you can push hard, and when you see enemies coming, you put a murshrooms in a triangle and get invisibility. when enemie or enemies push the lane, they will explode your mushrooms, you wait for 2 or 3 seconds, use your Q to silence enemies and jump on them and kill that guys, and go back for push lane. and do the same all the time. keep dragon and baron warded with the mushrooms, if is possible , red's and blue's buffs.