How to find the thief? Should i report this to police office of my city?

I bought an iphone 5 from a guy that I found on craiglist for $300. He said it was factory locked not user locked. Factory locked can be unlocked for like $75 but user locked can't be unlocked. When i took it to store it was user locked and i can't use it anymore. I googled the phone number but can't find any history of the number. It looks like that guy stolen it and sold it to me. Should i report to police? Can they do something for me?

Added (1). I live in los angeles.

Report it but I don't know if they can help or not.

Yes, report it.

They can't pay you for it or fix it, but they might catch the thief and you'd have the satisfaction of knowing he got what he deserved.

Report it, next time have the phone tested or call the carrier with the imei number and make sure it's not blocked.