Teemo might be better as a melee champion.
Let me just say that I love Teemo. The idea of playing a hamster death predator fills me with joy inside.
The problem is that he is currently too simple with gameplay that comes off as annoying to enemies. It's too easy to bother low-levels, and it isn't useful enough to work with higher-level play.
If he becomes melee, more damage and gameplay opprotunities could be provided that isn't one dimensional or toxic. They could push the hit and run tactics if he was running around throwing traps and mines everywhere,ambushing enemies and leaping all over the place.