child born 12-19-1977

looking for my birthchild born in NY on 12-19-1977, but adopted out of state, possibly in Nevada. the birth mother did this without my consent, I've been searching for the past few years, Lawyers told me I couldn't do anything until my child was 21. So i started looking, My child has 3 half siblings that want to find their older brother or sister, can anyone help