I agree with YorkieRose that it's very rare at 12 weeks to have a trained yorkie. A dog trainer told me once that puppies do not have muscle control until they are 6 months old. It sounds like you are doing everything right. The one thing that worked for us was taking our pups out every hour. Most times they would go, but there were still accidents in the house. But lo and behold, when they reached 6 mos., there were fewer accidents and eventually they were housebroken.
I wouldn't expect too much at this stage. You've got a few more months to go!
