How can I get post adoption visistion rights after 6 years?

My parental rights were terminated when my daughter was 6 years old due to my drug abuse. At the time I had no knowledge of appeals court or anything else and was made sign a paper saying I would give up my parental rights. I initially refused to, but was threatened saying if I did sign the paper I had a chance to still have visitations but if I didn't they would make sure I never see her again. Being young at the time I had no idea what was going on only acting on interest of being with my child whenever I can. This all happened in 2004-2006. Since then, very recently I have gotten in contact with her via facebook and other internet sites. Her best friend has called me and we talk also. She is very anxious to see me and is very happy to also hear from me but extremely scared to contact me herself because she doesn't want to get in any trouble by her foster/adoption parents. Is there a way we can resolve this so that we can see each other again?