If you like the dude, pray that he gets saved. Until then though, stay strictly platonic friends. Do not think that you can be a better witness by being his girlfriend. I've seen many young Christians, mostly women for some reason, that will date a nonbeliever, get really close, and then make a condition that he must be saved in order for them to get married. The boyfriend will usually gets saved so that she will marry him, but the only reason that he did it is usually just so that she would marry him. The problem is that his only incentive for getting saved was so that he could be with the girl, so there is very rarely any spiritual growth. This causes the woman to be the spiritual leader in the relationship, and the dude is a baby in Christ, and never grows. This is the spiritual equivelant of a 40 year old marrying a 15 year old. This is still unequally yoked. I know it sounds sexist, but Corinthians makes it quite clear that the man should be the spiritual leader of a household, and while you're probably not thinking of marriage yet, it would prove wise if any potential husband was spiritually mature, and had the same understandings as you about things.
Now, if you have an interest in this dude, it's not impossible for him to get saved, and reach the same spiritual maturity as you. I've seen it happen to people very close to me, and now they're happily married. But I think you should wait until he's saved before you become more than just friends. If your church has a youth group, invite him. He would probably only go to hang out with you initially. Eventually though, he might hear the right message, and get saved.
