I'm going to agree that you should just talk to him. Sooner rather than later.
Personally, I would find looking around online trying to find something he did wrong as a breach of trust in the relationship. Why didn't you just ask him in the first place instead of going online to check up on him?
Also, like others have mentioned - there are various reasons why he may not be listed as in a relationship. Whether it's because he didn't think he'd get any attention if he admitted it or they don't have the option or he didn't know how. The only way to know is to ask.