Friend has disappeared

I have a friend to whom I am very close (but whom I've technically only known a few months). He lives in my university city and I've left for the holidays, but we've been in frequent contact (at least a couple of text messages per day) and everything is good. A week ago, I texted to ask how his day was going (as usual) and got a reply saying that he was tied up and annoyed about something so he would text me later. Since then, I've heard nothing and I'm getting really worried about him. This is so out of character; he's not a player (and we're not romantically involved so it's not anything like that) or flaky; he's a really decent guy and I can't think of any reason why he wouldn't at least let me know he's okay. As I said, I'm really worried about him and I'm thinking of contacting his boss to try to find out if he's ok. We have no mutual friends so I can't think of anyone else I could ask. It seems really drastic though; any ideas on what I should do?

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