frosty fist for the peels
I was going to respond that you don't have many in-combat abilities to use as teemo, so you would not be getting many IBG procs... but I guess plopping down a shroom will cause the trigger, and the slow from it would be perfect to ensure the shroom to hit, too. So I would have to think about that.
As toplane bruiser teemo I like to get Frozen Mallet, but since that is one of the most expensive items in the game, I am not as sure about it for supporteemo. Especially since hp is a stat you will get from various items anyways (hi sightstone, hi Liandri's, hi potentially Locket)...
The cdr and mana would help in causing global shroomification as well... I need to try this!
So. FCQ, SS, boots, IBG, Liandri's, Locket as the full 6 item build, order to be determined by various other factors.
Mikael's might be another option, either alternative to Locket or as a replacement for FQC... man, so many options...
As much as I like spooky ghosts, I am not sure I would have the space for them in a supporty teemo build. Then again, I guess you could go for more of a damage build in which the goasts would work better, but... hmmmmmm...