Hopefully at some point the father lived in the US for a year at some point in his life, otherwise there is no way the kid is getting citizenship.
You need to provide clear and convincing evidence that the US Citizen is the father. Presumably your US court ordered paternity test suffices of that. Information on the forms and how to file them are here: http://www.uscis.gov/policymanual/HT...-Chapter3.html

