My experience is a mix of this and brunos's. I've found that when you lose something omboard either the crew finds out right away and can identify owner and then they contact you immediately, or they either dispose or pass on to airports l&f. I don't believe any European airline run their own in house l&f service not even at hubs so guess that even if the service worked they would probably only pass on the message to others. So I'd personally try both le club or the airport where you were landing (if it was an F flight I imagine that contacting a specific f team might lead to better results.)