Welcome to YT
Generally speaking, yorkies are fully grown at around 7 months. I feed my little guy(5months) 1/2 - 3/4 cup of food per day. He is usually satisfied with this and there is usually some kibble left over. The key is to feed a premium dog food rather than a supermarket brand that way, they eat less but get more nutrients. There is a list of dog foods in the General Section called Whole Food Journal list of good dog foods (or something like this) posted by another member. These are the foods you should be feeding pup. I feed Natural balance and my pup does very well.
Good Luck and post pics soon