Years ago whilst boarding a flight back from CDG, a briefcase appeared in the vicinity of the door. Kept our eye on it then when boarding had finished and it was still there I made PAs asking for the owner, tried to marry up the initials from the briefcase with the passenger list. I walked up and down that 767 both aisles, walking back up backwards with the briefcase in the air, asking as I went, lots of smiles from the passengers and shaking of heads. Just after doors to manual the inter phone pinged “err have a passenger asking where his briefcase is”…. “If the pax’s initials are XXX, it’s in CDG”…
In this situation you did as much as you could, but unless anyone actually takes ownership, it won’t be staying on.