No reputable breeder will produce a toy or teacup anything.
The Yorkshire Terrier Club and AKC have a published standard, and the miniaturized versions of that dog would not fit either one.
Whenever anyone makes a point of producing a dog that is not within the standard of a breed, all other characteristics are abandoned in the selection process in order to get the size they want. That includes all the genes that provide healthy, happy dogs that can reproduce by themselves normally.
If you want a good dog, go to a good breeder. They won't be making anything otehr than standard Yorkies.
