There may well be charges that can be filed against the individuals who intentionally "hacked" an account, or used a password they knew they had no permission to use, but it is very doubtful that the local police or the feds are going to pursue this.
Contact Facebook and with the on-line game company and see if they can help you out. You can certainly contact the cops, but don't expect too much from them on this even if there is technically a crime that can be articulated. I know that my agency would not pursue it, and most do not have the capability or inclination to do so for something like this. The cost of the investigation and extradition of any suspects would far exceed the very minimal loss.
Sorry.
- Carl