It seems each character's voice actors have played roles similar to the ones they play in the game. Ned has played morally challenged characters like Michael and OG Solo has played gangsta types like Franklin. Maybe we should look for guys who have played roles like Trevor, and who happens to look like him (just like how Ned looks like Michael and OG Solo like Franklin). Here's are all the pictures we have of Trevor (feel free to add the ones I might miss). These may help the search:
Here are some sound clips of Trevor's voice, thanks to deffpony: Click.
We MUST find out Trevor's voice actor! It can't be just me that wants to know, right!? We've got Michael's and Franklin's... now we need Trevor's. Of course... it could just be my OCD. I will be rewarding the person who finds the voice actor a special signature. So perhaps that will motivate you guys just a bit more!