I just recently found this fantastic toy which comes in a shape of a ball where you can insert treats for your yorkie as well record a short message on it. Everytime your Yorkie touches the ball he will hear your personal recorder message and if he is smart enough gets a treat as well. Of course you can also switch of the voice option which motion sensored.
Fantastic toy, my yorkie loves, unfortunately this product seems to be more widely available in the US and therefore I´m unable to get this Teddytalktometreatball for my yorkie :-(
Have a look:
www.talktometreatball.com