If he isn't in any of you're classes, it doesn't mean you can't like him! I had a crush on a girl myself who wasn't in any of my classes, but to this date we're like best friends.
What I would do is see what he does after school, or atleast try smiling to him in the hall way, and see if he comes to meet you c:
What I would do is see what he does after school, or atleast try smiling to him in the hall way, and see if he comes to meet you c: