He's universal. As top, he can harass the tanks.
As jungle, he ganks decently and has great damage once you finish his first item.
Mid isn't recommended since most champions there are burst mages, but against
and
, he does alright.
ADC, well... I wouldn't recommend AD Teemo, but before Season 6, I got to level 5 as him playing him APC. Worked quite well, but not anymore (The secret is because BF sword were that expensive AF 1550 gold before while NLR was 1250).
And support is easy. Get spellthief's, blind the adc, poke whoever your adc focus and you should be golden or dead. And shrooms are great to keep your lane off ganks for you AND your carry.
He's a jack of all trades with little potential to carry, which is why most ranked games don't take him.