oh no thats horrible news
Since hes so small & quite old, do you think he has gotten stuck somewhere on your property or neighbours property? he could have fallen into a hole, or trapped under a deck.. any pools near by? as he could be stuck in the fencing.

Does he have aother doggy friends that he goes crazy for or they go crazy for him? Thats how we tracked down my friends lost dog, used my dog to hunt her down & he let us on a 2hr walk & right up to the house she was in She was safe & sound, it was a weekend so they couldn't bring her to the vets office to find her owners.

I'm sure if someone found a small old pooch, they porb took him inside & due to the weekend we're un able to take him to the vets office.. I;d check the vets offices tonight & the shelters, just incase. I've learned that because you call once, the shelter might not call back if the pooch arrives, esp if they are busy or forget about the look out... Always best to call daily to check in or go in yourself & take a peek every other day.