[MeganS]

Put up Fliers. But don't put a picture of him on them. Put a (simple, general) description of him. Put the fliers around your neighborhood, in any shelters in your area, vet offices, Targets, PetCos, etc.
When/If people call, ask them to describe the dog for you. Or ask for a name and see if he responds.
Also, try calling the local shelters, etc., to ask if there have been any reported missing yorkies. You might take him into the vet and have a scanned for a microchip. And one other thing (that's kind of far fetched...but probably worth a shot) is if you put a leash on him and take him out for a walk, say something like "Let's go home," and see if he takes you to his home.
Good luck!