Per a reader:
The dog was found with a necktie as a makeshift collar and a chain as a makeshift leash. No real collar or tags.
The girl who found him asked around the dog park if anyone recognized him, but none of us did. He didn't look that old and seemed in decent shape (like he had been taken care of) so maybe he was lost vs. abandoned.
The person who found him will take him to a vet to see if there's a chip...
Updated:
The vet didn't find a chip. The dog is currently in a loving foster home.