maggie wouldn't eat anything at all when we got her but we bought a bag of royal canin and she went nuts for it. she loved it. i have to say, it does smell pretty good
just do all you can to make him eat. my vet said baby foods such as chicken or beef. some people have told me cottage cheese. I have heard of boiled chicken and rice but maggie wouldn't touch that.
don't let him over play especially if he is not getting nutrients that he needs. you have to be so careful with these little guys, especially as young as he is. we almost lost maggie, she was 11 weeks old and wouldn't eat. her blood sugar was so low, she was practically dead. we gave her some honey water and she bounced right back and I was bound and determined to make her eat.
good luck to you. let me know what you find that works. try the royal canin puppy food. i bet he will like it.