You are an angel for giving this pup a safe haven
People on Craigs list have been known to do some very unsavory things to get a hold of a dog to either abuse (like sell to backyard breeders) or resell for money.
If you can find any markings or such on the dog that only his owners might know about about would be a real help in your search.
Please keep us on Yorkietalk informed and we will help you.
Thanks again!