how to fined out what has happened to a child

me and my ex partner spilt up sometime ago and she moved away with my children i only no the area she lives but i dont no where. I got in contact with her on a social network. On her photos on the social network site i only found pictures of 2 of my children but the latest picture i found of my 3rd child was in 2008. I asked her for some more recent pictures of my daughter but as soon as she found out i was back with my partner now. She has blocked me on the website i dont no where to go from here to find out what has happened to my daughter as i no she has disabilitys can you give me advice where to go from here