We treated litter box training just like you would the puppy pads. We put a box in her cage and we also put one in one other place in the house. Everytime she acted like she were about to use the bathroom, we would scoop her up and put her in the box real quick and then praise her and give her a treat for using the box.
In the case when she would pee on the floor or in her cage, we would of course rub her nose and raise our voice which scared her (never hit because her little hips are fragile). Then we would take her to the box and speak in a high pitched happy voice and give her a greenie treat.
Instead of cleaning up the pee accident, I would take a maxi-pad and soak up the pee and then stick the pad to the bottom of the litterbox and bury it with the litter, so the scent would be there. If she pooped on the floor, we did the same thing and picked up the poop and put it in the box.
She caught on very quickly. Now, she still had accidents on occasion, but I believe that's the nature of yorkies. She's four years old now and she might have two accidents a year, and once of those were probably our fault for accidently leaving her cage door closed.
It's been such a great solution for our situation, because I always worried about her being so little and hurting her bladder holding it so long. It's also nice not to have to take her out every-so-often, or in the middle of the night. She knows that she can go the bathroom ANYTIME she wants. We often watch TV with her laying beside us on the couch and she will disappear for a few minutes, go use the box, and come right back. SOOOOO easy!!!
I would recommend it to anyone! Good luck!