First of all, about this website and this board:
I cannot help you with catching and prosecuting scammers!
This site is for educational purposes only: to expose scammers and make sure other people don't fall victims. This is more like for prevention of scams. I am not connected in any way with authorities, FBI, detective and investigation services. I cannot help you filing complaints, reporting and investigating.
If you are a scam victim, still in correspondence with a scammer and if they know any personal information about you, like your real name, phone number, address, etc..., the first thing you should do is DROP THEM. Stop all correspondence, block them from all your messengers, don't reply to their e-mails, don't answer their phonecalls. Many people are tempted to keep correspondence in order to "get more info on the scammers". Not only it is not safe, but sorry to say, in most cases it is useless! If you think that if you collect enough "evidence" they are going to be caught, and you will recover your money, sorry to disappoint you but this is not going to happen, especially with Nigerian scammers. No matter how much info you collect on them, most of this info will not result in their arrest. Unfortunately, your money is gone. Stop correspondence, close this page of your life ASAP and move on! Leave the job of collecting info to scamhunters.
Another thing to mention: never provide scammers with links to scamlists where they are listed. First of all, by doing so you are educating them, they will just change their aliases and continue scamming under a new name, so basically all previous hard work in exposing them will be in vain. Also, sometimes people who report scammers leave their real names and e-mails, and you will be putting them in danger of "scammers revenge". People obviously don't like it and may stop reporting.
One good news is that your loses may be tax deductible. Consult your tax accountant for more info.
Where to report? First of all, you have to understand that if your scammer is overseas, most likely he will never be caught and you will never recover your money. The reporting is just to bring attention to the problem. Also, a scammer might be using mules in your country, those should be located.
http://www.ic3.gov/" onclick="window.open(this.href);return false;
http://www.efccnigeria.org/" onclick="window.open(this.href);return false;
Don't expect a reply from them, though.
Also, if you have sent money, please report to your local police. You will need a police report to claim the loss on your taxes but also if you cashed a forged check or forwarded stolen property you should also report to the police first before they come looking for you. This will go along way in helping you avoid appearing as an accomplice to a crime.
And finally, please report them here on Romancescam.com. This is the MOST important thing you can do, by doing so you will be saving many victims and hurting a scammer where it hurts him the most - in his wallet.