No luck so far, no contact from owner of the little lost chihuahua. I will put flyers on the street where I found him. I do not think he wandered far (if he wasn't dumped).
My initial estimate was that he belongs to an older person who did not have the energy to care for him (dirty, needed brushing, nails badly overgrown) but showed love by feeding too much.
I am reluctant to hand him over to animal services because they take legal possession in 3 days AND they're 25 miles away.