There are many different types of fraud and each may be reported differently.
First, report the fraud to your local police department.
After they establish some lovely correspondence with you, fall in love and maybe even send a couple of cheap presents, they will either: a) be almost on their way to meet you, but something will happen to them: they will get robbed, beaten, get into the hospital, or other misfortune will happen and of course you will be their only contact to ask for financial help, or: b) tell you that their employer pays them with Money Orders or checks, and they can't cash them in Nigeria.
They will send you the Money Orders or checks and ask you to deposit them into your bank account and then wire the money to them via Western Union.
Equifax, one of the three major credit reporting agencies in the U.