Yorkies and Silky's are often confused with each other, for a few reasons. A Yorkie's hair is often called 'silky' so people get confused, thinking they are the same breed, etc. They look sooo similar. And there is so many backyard breeders and puppy mills shelling out these dogs (since Yorkies are so popular) so the breed standard is often not met. Yorkies come in all shapes and sizes and just because a Yorkie is larger does not necessarily mean he's not a Yorkie. Yorkies used to be bigger back in the day so some just carry that gene still. A yorkies parents can be under 7lbs but a pup might end up being 10lbs or larger, it's so hard to know or guess.
Here's a good comparison:
Home of the Gorgeous Silky Terrier!! - Compare the silky to....
I tend to think my Jackson is a Silky or atleast Silky/Yorkie mix maybe but I really don't know. He was sold to me as a Yorkie. He's 16lbs and to me has the body of a Silky more, but maybe more of a Yorkie face. Properly bred silky's and properly bred yorkie's are easier to differentiate. Another problem, I've heard of alot of folks that use Silky Terrier females to breed with Yorkie males because a Silky is larger and may be less complications so that's another problem is people going around selling Silky's as Yorkies.
The Silky Terrier is a true "toy terrier". He is moderately low set, slightly longer than tall, of refined bone structure, but of sufficient substance to suggest the ability to hunt and kill domestic rodents. His inquisitive nature and joy of life make him an ideal companion. The keenly alert air of the terrier is characteristic. The manner is quick, friendly, and responsive. Approximate size of a Silky is 9 to 10 inches at the shoulder height. They are of a fine bone but maintain muscle and strength of a much larger dog. They do not think they are small but a large dog in a small "suit." The Silky may not be the breed for every home. You must be willing to add another intelligent being to your family as a Silky can be much like having a toddler child loose in the home. They do not like being neglected or forgotten and if left alone for too long a time they will find entertainment that may not be to your liking! A Silky isn't hyper but they do have tons of energy and love to play fetch, go for long walks and in general, be involved in whatever the family is doing! They are loving but independent in nature. They are not generally what are considered 'lap dogs'. Small children do not do well with a Silky due to terrier nature. Food in the hands of small children is fair game for a Silky as well as chasing their feet when they run. Silkys are mistaken for Yorkies sometimes, but they are much more like their cousin the Australian Terrier.
First pic is Silky is show coat.