Thank you so much for trying to help reunite this gorgeous baby with his person. Perhaps check with vets in the area to see if they have a client that has lost him, or maybe have a record of a bird with that band number.
You can put out flyers, or post on social media, but don't post anything about the band. The rightful owner should be able to provide some kind of matching information to prove ownership. Beware of scammers looking for a free bird that isn't theirs.
Good luck, I hope you can find his person. You're right, someone is surely missing him.