How do I locate some one with only thier first and last name?

Well about three years ago my mother died and she died an adopted child not knowing who her parents or anybody biologically related to her was. The adoptive parents (my grandparents) went missing after my adoptive grandmother died. I havent herd from my grandfather since my mother's funeral and im almost 18 now and Im really looking for answers but all I have on my grandfather is his first and last name and there's a possibility he is in 3 different states. I dont know where to start , so please someone help me out.