Probably was listed at one time, and then the listing was withdawn, or expired, or even sold. Searching for real estate on sites like Trulia, Zillow or Realtor.com is NOT the best way to go about buying a house. These sites do not have the most up to date information.
You need to find a local REALTOR to work for you as a Buyer's Agent. It doesn't cost you anything. He/she can set up a search in the local MLS and send you ACTIVE listings that fit your needs.