My brother had a friend that would always steal his stuff when they came over, but this was back when they were like 10. We never really confronted them about it because it just makes things messy, they just kind of grew apart as he realized that it seemed his friend was just using him for his stuff. This friend of yours sounds like a similar kind of situation, but in adult form, which truly surprises me. I could not picture any of my friends in their 20s stealing stuff from my house, they have jobs, they make money, and they are good people. As people have pointed out, it could be an addiction of his, and if that's the case, he needs help. This is one of those situations where, since he IS a friend, you have to at least talk to him first. If he truly is a good friend, he will tell you what he has been up to and why. If it is because he needs money, find out why, especially if he has a job. If it is because he can't stop, make him get help, if it is because he wanted them, tell him to eff off, because I'm sorry, but that is no friend.
That's my advice, in my personal life I have a very small circle of friends that I actually hang out with in a social manner. Only a couple do I have over my house, this is because the others have questionable habits or personalities that I have personally picked up on that I am not sure many notice. It is "normal" to everyone else, but to me, their behavior is destructive, or just plain annoying. I hang out with them at work, or will talk to them in stores, or on Facebook, but will NOT invite them to my house. You have to be able to discern, so that is my second leg of advice. Good luck! I hope you figure it out, keep us updated please!
NNID: Dongo8 XBL Gamertag: Dongos Revenge
