My guess about that picture you keep sending around, and the person to whom it belongs, is that he is someone who tried to help you in the past, but realized, after awhile, what a leach you are. He probably picked you up while you were hitchhiking and let you stay in his home, at which point, you discovered some minor secret in his life. You left, threatening him, and attempted to use that secret to blackmail him....am I right? But then he decided not to respond to your threats anymore, and now you are trying to make his life miserable. If his identity was actually a mystery, as you say, you probably wouldn't have such a clear picture of him. That said, you need to butt out of the missing persons case to which you have claimed that he has a connection. All you are doing is interfering with the investigation and running a serious risk of causing harm to someone who isn't even involved at a bystander's level. But then, that's what you told him you would do if he didn't pay you, isn't it?
If you either know, or seriously think, that he should be investigated, go to the police. Don't send his picture to everyone you can reach via the internet. And stop threatening people. Just come forward with what you know, if anything, and stop blackmailing people.