I agree, as attached as you are already, he might be microchipped and belong to someone, who i HOPE is worried sick about him. if not... you have THE best breed you could ever ask for
he is sleepign because he is stressed out! poor little guy. I would be offering him small amounts of food frequently so his tummy can get used to having food in it. keep in mind Yorkies have sensitive necks and you should use a harness instead of a collar. Also if it is cold there he should probably have a sweater on when he is outside. I also agree with the vet check.. make sure he has no bugs.. if he was out for long enough he may have drank bad water... after that.. watch out.. he is going to steal your heart and you'll have no idea what hit ya
can we see pictures?