I'm still thinking a Yorkie/chinese crested mix. A Chinese Crested is a toy dog and not that much bigger than a yorkie(of course just like yorkies you will see them in all sizes). I believe cresties are supposed to be between 5-12lbs on average. Here is a couple pictures of the mix
http://www.dogbreedinfo.com/c/crustie.htm They all look very different from each other. On the crestie/shihtzu mix you can see a pic of a dog with the coat pattern like yours (hairless on back)
http://www.dogbreedinfo.com/crestedtzu.htm
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~Magnifique Yorkies~
Purchasing from backyard breeders, pet shops, and puppymills perpetuates the suffering of other dogs.
Educate yourself and buy from reputable breeders or rescue.