How do you find a famous person?

[Nobody.Nothing]

I am going to America for a holiday soon (mainly in New York) and I would really really really want to see my most favourite actor. How do I find him? I can only tweet to him through twitter and he may not even get any of my tweets at all as after all he is famous!! Although I did get a tweet from him once before... Also I know he lives in Los Angeles. When I'm going to New York so, how can I get to see him? I'm gonna be close enough (in the same country) and how will I know if he is in New York or not? Or whereabouts he is?? I know this may sound impossible but I'm really desperate, thank you.