It says in the CO that BM has discuss improtant issues about SD with DH. I would think that his daughter moving is an improtant issue.
BM isn't technically withholding SD from us. She and DH mutually decided to stop the every other weekend visits because SD was always crying when she was at our house and saying that she only wanted to be with her mom (this behaviour started after my MIL turned her back on us and tried to take our SD away from us by submitting a list of lies about me to the court on BM's behalf). They decided that visits would take place when SD asked to come to our house.
I understand why we don't see SD right now, it's because DH decided that it was better for her not to see him than to be absolutely devestated everytime she did, I just don't like that BM has made it so that DH doesn't know where his daughter is, and that she won't even read something that lets her know the whole reason that DH agreed to stop the regular visits.
You are right though, there is no point in me continuing to try with someone who cares more about herself than her daughter.
I will continue to keep SD and BM in my prayers.

I never thought of him calling the child support office, thank you

He has decided to stay out of the picture until SD WANTS to start seeing us again, it just bothers us that we don't even know where she is.

She used to LOVE being at our house and would frequently ask us why she couldn't stay with us all the time. Her behaviour at our house changed as soon as BM and MIL tried to have SD taken away from us. They both called CAS and made false accusations against me. CAS came to the house and saw that there was no reason for them to be here and have never checked in on us since then. When calling CAS didn't work BM and MIL then went to the courts and tried to have the CO changed so that MIL got all of DH visitations with SD and he would have to go to her house without me to see SD. The judge basically laughed at them when I had evidence to disprove each of MIL's 15 points on why I shouldn't be a mother (one of her points was that I made SD sit at the table for family dinner time even if she didn't want to eat and that it was abusive to force a child to do something they didn't want to do.....totally laughable). The judge ordered no change to the CO except that it was now police enforcable so they couldn't withhold her from us again. When we got her for our first visit after the court date it was like she wasn't even herself anymore. She spent the whole time crying and kept telling me that she didn't love us anymore and that she only loved her mom. She was NOT the SD I knew, she was a very sad child and not herself at all.

There was never a paternity test done although DH now thinks there should have been. He and I have 2 daughters together and both of them look like me and him. SD doesn't resemble my DH at all, and while talking to some of his co-workers he realised that there could be a chance that he isn't her father because his ex gf was away at school when she got pregnant. He didn't put a few suspicious things together until SD was over the age of 3 and we didn't have the money for a paternity test. Now he doesn't know if there is any point in spending the money on the test, because he has been her "dad" for over 4 years he could be ordered to continue to pay CS even if she isn't his.

The reason he isn't seeing her is because, and I am not exaggerating when I say this, for the last 10 months she was with us she was crying (or whimpering and trying not to cry) every minute that she was at our house and awake. It is hard to explain to people outside of our household, but it almost seemed like it was torturing her not to be with her mom. I am confident that she was either told lies about us, or made to feel guilty about being at our house because the change from happiest kid ever to the saddest literally happened from one visit to the next. I would also like to note that, because of the type of person his ex gf is, we made sure that SD was NEVER alone with an adult while in our care. There was no way we were going to risk her making false accusations against us (she had hinted that she was going to) that would ruin our family and get our girls taken away.
DH would rather SD be happy and not see us, than devestated everytime she does. We have kept everything of hers and set it aside for when she comes back along with other special things. There is no doubt in my mind that she will know we have always loved her when she starts coming over again. She will also (when she is old enough) be able to see all of the documentation on how hard we fought for her. We probably won't let her see the details, but she will see that for four years we were in court fighting for her. I hope that she is back in our lives long before she has children, and until she is back I will keep her in my prayers.

Thank you for your support.

We have been preparing ourselves for when she comes back and making sure that we have a whole box full of things we saved from her. We are also prepared for her thinking DH didn't want her or love her. My husband is not the type of person to put up with his kids being disrespectful him or to me. If she comes back and refuses to believe anything we tell her about why we didn't see her and treats our family like crap.... well I can tell you she won't be welcome in our home for long. If she is respectful no matter what she thinks or feels, she will always be welcome in our home.