If he is chipped you will get him back as soon as someone takes him to the Vet or ARCA. Sometimes when my dog has run away you get people who grab him, feed him for a few days and get in contact to claim a reward, others just think they have luckily "found" a new valuable guard dog/pet and keep them till they need to take it to the Vet, then act innocent when handing them back...

Either ways, good luck and do not give up. Mine came back after a 4/5 month "Holiday" this Summer.