Teenager's friend wants to move in

My teen has a friend from school that texted today asking to stay at our house. I have met this kid, but I don't really know him well. I don't know his mom, and I'm not getting a very clear explanation about why he feels he can't stay at home. From what I can gather he isn't in any danger and he hasn't been kicked out. He is staying at someone else's house right now but it's crowded and he's unhappy there. I'm inclined to say no unless he's in some sort of danger at home. Or maybe I should offer to talk to his mom? Ideas? Input? Thoughts?

*update*

We invited him over to hang out for the day today and stay for a sleepover just for tonight. Then we (my husband and I) will talk to him about his situation to see if we can find out more.