I know this post might be for the toy Forum but its something I was wondering other yorkie owner have tried.
My Buzz would love to play with my cats toys.

One day I went and got a toy mouse for buzz and let me tell you He loves it. I took a sqickie and installed it inside of the toy. He walks around with it and brings it to bed with him. He plays with it all day. I know that the yorkie was used to hunt mice. So I think they have a connection to them.
Try getting a toy real looking mice that does not have Catnip in it and give it to your yorkie and see what happens. Or does your Yorkie have one?
Please let me know or is it just my Buzz that is as crazy as me?
The Legacy of the Yorkie:
The Yorkie was bred as a ratter, used to kill mice and rats in small places. There is some evidence that they may have been used for hunting as well. Like most terriers developed in the early 19th Century, it was common for Yorkies to demonstrate their prowess as vermin killers in what were known as "rat pits." The terrier who killed the most rats in the least amount of time was considered the winner.
As a hunting group, terriers specialize in pursuing animals (usually vermin) that live in dens or burrows. Animals that are cornered and defending their young will fight ferociously. Therefore, any dog that would willingly pursue them must have an extraordinary degree of courage; terriers are bred for that quality.