Calling the sheriff would be the first thing I would do.
Vets and all the Animal Control folks next, in case someone called him in as missing.
Even though he is in great condition, don't be surprised if he was dumped
I rescued a dog in 2009 that was in excellent health, was house broke, loved a bath, knew basic obedience, yet the woman was observed dumping him. The witness thought she was merely leaving the dog out of the vehicle to do his business --------------- until the witness came back thru from work that night and the dog was sitting at the corner of the state highway waiting on her
He is still holding down the recliner, is at the top of the list for intelligence and learns in the snap of a finger, does not have a mean bone in his body, gets beat up by the cat, yet his 90 lb self is a great watchdog. I'd take five more just like him, if I could find them and I've been rescuing dogs my entire adult life.
She was "business dressed" and in a newer, very clean vehicle, so go figure why apparently intelligent people do such "I-hope-you-rot-in-****" things