[All_That_Chaz]

I feel like on-hit teemo is really good and should find a place in the meta and with the lane-swapping going on, I feel like there's an opportunity for him to find it. Teemo should have the upper hand against most bruisers due to his Q mitigating trade damage. He can also function as the team's adc by lane-swapping to top, taking away his weak early game.

Core Items:
Boots (merc treads/zerk greaves)
Blade of the Ruined King (true damage)
Runaan's Hurricane (apply on-hit effects)

Other possibilities:
Wit's End
Liandry's
Malady
Frozen Mallet
Warmog's
Sword of the Divine
Zephyr
Black Cleaver (if you're on a heavy ad team)

I would play him 9/21/0 but I haven't tried anything else.

As for team comp...
If he's top, he doesn't provide a front line or initiation so other roles will need to fill it. Junglers like Jarvan, Xin, and Maokai can fill this role well. Supports like Leona, Alistar, and Thresh work too. And if you have a diving mid like kha'zix, panth, or a ballsy TF, they can initiate. You can do different things with your adc because you have a ranged top. An Urgot could do well as he'll have less heat on him.
If he's adc, you should probably lane-swap. You'll need a more damage heavy team in general because teemo can't hyper-carry late game. Carry junglers like Vi, Elise, or even Fiddle could appear here. You could also throw Elise top. You can put many different people top because you're using a more tanky teemo who won't go down as quickly. You can go AD Renekton or Carry Jax.

As for what he brings to the team, his on-hit stuff with runaan's in a teamfight is stupid. You want to keep people clustered so runaan's will hit multiple targets. Jarvan and Thresh are great for this (especially together!). Stay away from Gragas, though. He can also provide tons of vision around the map. Yes, it only helps when the mushrooms are stepped on, but it's more than nothing. You can cover more ground with them and it can really help when you're behind and can't afford to spend money on wards.

Thoughts?