Sorry for the 2-month delay in answering a valid point you made!

I did add Teemo into the matchups. I personally find him to be a fairly easy matchup for Thresh. The early game is the hardest part since you have to deal with his poison without any sustain except for a Health Potion (not taking into account Font of Life, Absorb Life, or Fleet Footwork, as the first two don't even provide a noticeable amount of sustain).

Anyway, playing safe and trying to farm is mostly what I do if the Teemo is aware of his existence. When you drop below 50% HP, a lot of players tend to get super aggressive, so you usually have to be wary of that and try to take advantage of it. Getting either Heartsteel or Titanic Hydra is a big powerspike for us, and if you aren't behind, you should be able to beat him 1v1.

I hope this provides something useful for someone.