How to help someone your worried about..?

So I know this guy in one of my classes this semester at college. He was always kind of a quiet guy and kept to himself for the most part. I noticed that he would always wear clothing from an anti-suicide advocacy group, and I always kinda worried about the guy. He never really looks happy, and when i see him around campus he's usually alone, and it worries me that he might not be ok,or that he might end up hurting himself... I barely know the guy, just basically his name, but my question is: would it be totally absurd to just tell someone that you care about them, and if they needed someone to talk to, that you'd be there for them? I'm a bit nervous that i'm just making assumptions and i hate that... but at the same time, I feel like i'd rather tell him and be wrong, than say nothing and be right..