Sadly, most internet searches and classified ads are put there by backyard breeders and puppy mills. If you are really interested in a Yorkie that is close to meeting the AKC standard for a Yorkie then visit a breeder that actually shows their dogs. Now, I am not saying that everyone who shows is necessarily reputable but you have a better chance of finding a good one if you go to your local AKC sanctioned dog club and ask for their breeder referral person.
The people who belong to these clubs are trying to meet the standard as closely as possible and many of them are very serious about preventing genetic defects and other weaknesses that can occur in purebreds.
Here is a link to the AKC club search page.
American Kennel Club - Club Search and Directory
Most clubs list the breeder referral person right there on your search results.
Do a search for a conformation club in your state or surrounding states. You can also check to see if the state has any Yorkshire Terrier clubs. The YTCA also has a website that will give you some good information about what to look for and of course if you read the "sticky" areas here at YT you will find helpful info.
Right now small dog breeding is at an all time high in this country. The increase, however, has not been in knowledgeable breeders that understand the genetic difficulties of breeding purebreds. The increase has been in home style breeders and puppy mills that will breed any apparently purebred dogs they get their hands on.
Purebreds are genetically manipulated dogs. It takes many generations of experimental breeding to create a purebred that will consistently reproduce uniformly. It takes only on or two generations of poor breeding practices to cause a purebred to deteriorate from the standard. That is why you see so many purebreds that have attributes that are not at all like the breed standard. You will see Yorkies with floppy ears and under or over sized. Large eyes and short noses are not in the breed standard. These may be very nice pets but those who breed a Yorkie to look like that are playing with fire. Genetic defects abound with that sort of breeding.
It is a good idea to go to some dog shows. They are fun for dog lovers and you can learn a lot. Go to at least two or three breeders and look at their dogs and observe how the dogs are kept. You will see a lot of variation but you should always see dogs that are happy and healthy as well as well cared for.
A bad breeder will have too many dogs and lots of cages.....OR.....they will not allow you to see hardly any of their dogs and will only bring out very few pups or maybe only one for you to see. That would be either a broker that works for a puppy mill or someone who does not want you to see the conditions their dogs live under. Never buy a pup or a dog from a breeder that wants to bring the animal to your home or meet you somewhere.
A good breeder will have lots of information about the ancestry of their dogs. They will have information about the genetic testing done on their breeding stock as well as plenty of show win pictures and trophies on display.
Learn all you can so when you go to meet a breeder you know what to ask for and also so you know what you are looking at.
Good luck on your search. Hopefully your new Yorkie will be with you for many, many years to come so take your time and get just the right one.