That plane is certianly long gone from Dulles, so if it wasn't found while there, the lost and found at another airport may have it. Unless the airline has a central L&F. You don't say where you are. If going to Dulles is not a burden, sure, go and ask, but first confirm that the airline would give it to the airport's lost and found (along with items found in the airport) and not put it in their own baggage or other offices. If it was stolen by a cleaning person, or another passenger (on the same or subsequent flight) or someone else, what could you, or anyone else, do at this point? Don't expect the airline or airport authorities to start questioning all cleaning personnel and everyone else who had access to the plane. You don't know what happened. No secret remedies, sad to say. Good luck. I left a digital camera at the domestic airport in Buenos Aires (pretty sure a guy sitting near me took it as I was rearranging a bag's contents-- my fault for not paying attention). Never got it back.