How do i get child support from a man that i dont know where he live or what his name is?

i know his facebook but it aint his real name on facebook and he wont tell me. he said if he gonna pay money he gonna see his kid but i told him no he aint and he gonna pay for his kid
Update: can i have the police or courts or someone go on facebook and make him give us his name and address and info? he would be legally obligated if the police ask him for it right? because they will trace where he lives
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