Dear Home Seller,...Not all web sites show all homes on the "mls". Also different states and regions have different MLS services. Since the MLS is a "private Realtor tool" each Realtor Agency can "opt out" or "opt in" to share their listings on any given web site. You are not saying which web site you are looking on, so I suggest you speak directly to your listing agent or their manager. One site you can try is http://www.realtor.com.
This site has much of the nations homes for sale. But again, let's be clear... not every home for sale is on every web site and yours may not be on realtor.com. Hope this helps. JT founding member of "houseJT' (Joe's Team to help you sell, buy and keep your home).