Hi The Fox & the Hound, first of all it sounds like you really care about what he might be doing, so respect!!
And I'd say, yes, talk to him. For all you know either no-one has shown a real interest or at least no-one he feels he can really talk to, and that has to be so isolating given the way he is feeling. With the chance that he may be sinking deeper and deeper without anyone at least "reaching out a hand he can hold onto". What you say may not work, but at least you'll have tried and at least hopefully he'll know you care.
Just don't be "full on", no "accusations", no "interrogations". Just maybe try to let him know that you've noticed, and some "if"'s in a supportive manner, and let him know you're there for him to start with. Or just think about what you'd like someone to say to you, if..........I wouldn't necessarily expect him to just come right out with everything, but if you've at least let him know that he can talk to you, maybe next time, or sometime...........
And again, respect for wanting to help him in this!!
Alison