This is the USA equivalent of the UK national Action Fraud organization. If you are based in the USA and have been scammed online contact these guys (http://www.ic3.gov) after contacting your bank and credit card company. Chase the scammers down good luck!
The site explains how to file a complaint, preserve evidence and gives advice on future protection.
Their own explanation of ic3 follows:
The Internet Crime Complaint Center (IC3) was established as a partnership between the Federal Bureau of Investigation (FBI) and the National White Collar Crime Center (NW3C) to serve as a means to receive Internet related criminal complaints and to further research, develop, and refer the criminal complaints to federal, state, local, or international law enforcement and/or regulatory agencies for any investigation they deem to be appropriate. The IC3 was intended, and continues to emphasize, serving the broader law enforcement community to include federal, as well as state, local, and international agencies, which are combating Internet crime and, in many cases, participating in Cyber Crime Task Forces.
Since its inception, the IC3 has received complaints crossing the spectrum of cyber crime matters, to include online fraud in its many forms including Intellectual Property Rights (IPR) matters, Computer Intrusions (hacking), Economic Espionage (Theft of Trade Secrets), Online Extortion, International Money Laundering, Identity Theft, and a growing list of Internet facilitated crimes. Since June 2000, it has become increasingly evident that, regardless of the label placed on a cyber crime matter, the potential for it to overlap with another referred matter is substantial. Therefore, the IC3, formerly known as the Internet Fraud Complaint Center (Internet Fraud Complaint Center), was renamed in October 2003 to better reflect the broad character of such matters having an Internet, or cyber, nexus referred to the IC3, and to minimize the need for one to distinguish "Internet Fraud" from other potentially overlapping cyber crimes.
IC3 Mission Statement
IC3's mission is to serve as a vehicle to receive, develop, and refer criminal complaints regarding the rapidly expanding arena of cyber crime. The IC3 gives the victims of cyber crime a convenient and easy-to-use reporting mechanism that alerts authorities of suspected criminal or civil violations. For law enforcement and regulatory agencies at the federal, state, local, and international level, IC3 provides a central referral mechanism for complaints involving Internet related crimes.
Significant and supplemental to partnering with law enforcement and regulatory agencies, it will remain a priority objective of the IC3 to establish effective alliances with industry. Such alliances will enable the IC3 to leverage both intelligence and subject matter expert resources, pivotal in identifying and in crafting an aggressive, proactive approach to combating cyber crime.
In the UK, for similar support, contact http://www.actionfraud.org.uk