Internet Fraud is investigated buy a division of the FBI. The FAQ's on their web site is full interesting information. Here are two I find interesting. Also it is very easy to file a complaint.
Q: Do you have a definition of Internet crime that I can refer to?
Internet crime is defined as any illegal activity involving one or more components of the Internet, such as websites, chat rooms, and/or email. Internet crime involves the use of the Internet to communicate false or fraudulent representations to consumers. These crimes may include, but are not limited to, advance-fee schemes, non-delivery of goods or services, computer hacking, or employment/business opportunity schemes.
Q: Can I file a complaint if I have been defrauded of money or goods?
If you believe you are the victim of an Internet crime, or if you are aware of an attempted crime, you can file a complaint on our website. Be sure to include as much information as possible about yourself (i.e. name, email address, mailing address, etc.), the perpetrator, and the Internet crime that you are reporting in order to expedite your complaint.