Talk to him about anything. I usually use the lines of "You look so familiar, do I know you from somewhere?" then you take it from there.

Don't build castles in the sky though; unless you are 100 percent sure that he is attracted to you, do not make a move; some guys will feel complimented when you tell them they are hot, some guys will get violent, so be careful. Also, because you are already biased about him and you are infatuated with him you may want him to like you and therefore, you will see things that are not there… don't make assumptions and just take it slow getting to know him first. Start with casual conversation and go from there.. yes, I know you want to rip his clothes off right now and make love to him, but remember this, Rome was not built in one day