First of all, is this someone from school? I completely understand that you'd feel uncomfortable just randomly going up to him and talking to him. What I suggest is finding something in common to start up a conversation then taking it from there.
If this is indeed at school, does he study in the library at all? Do you share any classes? If you are in sixth form do you see him in the common room? in any of these place you could go sit next to him, not necessarily go and straight up to him and say hi, I like you. If he is reading something, ask what he is reading as it looks interesting. Just an example but there are a few things you can use to break the ice and after that speaking to him again will be much easier. Once you're properly introduced you could get contact details and if he shows interest then perhaps try to take it further.
I know I'm making it sound much easier than it is, but I tell you if you don't do anything at all you might regret this later so at least have a go. Hope this helped.