What is considered child abandonment?

I need to know the guidelines for child abandoment by the father. My son is 17 mionths old and the father moved out of state and hasnt visited or cared to visit in 4 and a half months, and dosent plan to. He also dosent paid child support, never has. Before the father moved we had a legal contract about joint custody drawn up that he would get him every Monday and Wednesday for 2 hours and every other weekend over night, which obviously has been violated. What steps do i need to go about to gain full custody of my son?