8 weeks!? Oh wow, that's pretty young for the breeder to have placed him.
(Reputable breeders generally recommend waiting until around 12 weeks.)
Given his young age, for now, you should keep him on the food he was accustomed to eating while with the breeder. He needs a steady diet now while he is trying to adjust to his new home. The smallest things--a change of enviroment, new home, new food--can really throw these little guys for a loop. Research foods in the meantime and as he adjusts,
gradually switch him over and try new foods. Never swap cold turkey...it could easily lead to digestive upset and even intestinal infection.
Check out the Health & Diet section for more feedback. There is a sticky at the top with some of the more recommended brands for Yorkies--some companies will even send you free samples!
http://www.yorkietalk.com/forums/yor...e-samples.html
Also, since your little guy is young, look up the signs of hypoglacemia. (I can never spell that right.) Learn some warning signs and how to prevent it as Yorkies are prone to it when they are pups.
Welcome to YT!