What do I do to get my son back if the father will not let me see him?

My son’s father is a gambler and really controlling so when I was working on day he kicked me out of the house that his friend lets us stay. He would not let me see my child until we went to court and they gave him temporary custody. When the custody was up which was in August 17,2012 we had a verbal agreement of how things was going to go after and we wrote it down as well and had his sister and my sister signed the papers to make sure everything would run smoothly. Just so happens the holidays was coming around and this is the time I was getting nervous about how everyone was going to react so I noticed that when my son’s father goes to work he took our son with him and it would be in New York or New Jersey. In November it was thanksgiving and I didn’t get to spend half of my time with my son because of his family. I was calling my son’s father to make sure everything was still going according to plan but when I was not getting any phone call or text back I knew something was wrong so I had a policeman come over where his sister stay. I had my son the next day his dad came to my place of residence because we were suppose to discuss moving arrangements because I said I may be moving and so was he. Soon as he shows up he takes my son from me and drove away. I have not seen my son in about a year and a couple of months his dad moved away and will not return any of my calls or text. I need to know what to do because I was told everything that was going on in the house how people had to make him get up to feed my son and wash and change and my son was outside playing by himself while his dad was in the house the back room with the door close and my son went it the road and almost got killed by a car if it was not for his dad sister coming saving my son.