What can I do if my wife moved kids out of state and remarried without me knowing anything about a divorce?

We were separated almost 3 years ago. She took my kids and hid them from me because I would not financially support her needs. After I stopped giving her money, she no longer let me see my kids. At the time, we were still married and as of now, I thought we still were but separated. We both have other partners now. I now find out she remarried which I don’t know how if I never heard anything about me signing for divorce and she has recently moved to another state. What should I do? How can I get my kids back? I would question her family about her and the kids and they would say they have no idea. I talked to her over the phone about a year ago and she called me from a blocked number and she wanted me to sign my rights over which I would never do.