For the US residents:I assume the crime must have a 'US' element, or the US authorities won't touch it.
Since we're dealing with scammers, you need to know where the scammers are, so if 'Mary Chrissy Jenny' who is working as a model in Nigeria, but claims to be from Ohio in the US of A' scams you......it won't work.
Ask us where we think the scammer is from...
Basic rule of thumb, 'the scammer is where the money is picked up'.
Not always accurate. works 95% of the time.
Sometimes, Nigerians will have a victim or accomplice pick up money in another country.
If you've sent money to 'that country', you need to start with the appropriate Law Enforcement Agency.
Here's a the online form for the US.http://www.ic3.gov/