Apple has a program to find the iPhone. But all this does not lead to anything, usually. I know from my own experience. You can write a statement about the theft, if there are good friends in the police, then they will try to find it. Provided that you then declare to pick up: D there is an option to write a letter to the company, asking to block the device. But first, it’s better to know who uses it, of course, then politely ask to return: D type, anyway it's already a worthless piece of iron. Well, then unlock.
However, if the phone was stupidly reflashed, then this is unlikely to help. In this case, it will work only in Russia and that’s it.