How can I get child support from someone who is not paying.?

My daughter is 8 years old and he has payed child support maybe 3 times. I called my local office but they say they cant do anything without an address. I gave them his mothers and I guess she said he didnt live there anymore. I talked to him when I finally saw him and he said he is homeless which I dont believe because he is on facebook everyday. Anyway I feel stuck and dont know what to do. I know he has a job now because he bragged about it on facebook but child support has no knowledge of it so Im thinking he is working under the table in construction. Does anyone else know any other options I could look at to get the child support for my daughter? Thanks