Did you record the phone ID info and report it? An option would be to report it to apple first. (the unique apple device ID) If the new owner decides to use Itunes etc they may use their credit card. If you report it properly the device will just get locked out of a particular area's cell use. Not sure how this would go.
This is specific advice only for Steve Try ringing the phone phone first. Report the sim card as stolen only first. The see if apple can/will play ball and agree to notify you if devive get's verified online. To register the device requires a lot of identifying to register. If the new owner assumes that the purchase was legit or that it will work on cell network that it was never reported stolen and may risk attaching it to iTunes. Once Apple anknowleges that the device is active you then report that to Police. Report it stolen after say 1 month if no contact from Apple.