How Do I Contact Someone To Report Very Serious Defamation Of Character?

In your case you can look for a  Cyber investigator.  A cyber investigator is the one who track down a proof who is doing the attack. However, each of these has some serious consequences for you.  These will really happen here if :

1. You Want To Sue For Defamation: Assuming that you have a case because of the nature of the Facebook information, then if you want to sue the attacker, you are typically looking at a combination of both Cyber investigative work being performed as well as legal work. Totally, this can cost you in the 10′s of thousands of dollars (16K+) so you have to be very clear about why you are doing that and what you hope to gain. More than likely, you not be able to get a lawyer to take on a case like this on a contingency basis.
2. You Want To Stop Attack: This can happen in one of two ways usually. First, and always your first choice, is to try and find a way to work it out with the person who is attacking. Sometimes for businesses, it is cheaper to offer the attacker something of value to remove the info and stop that it is to go through other means. If this approach is not an option, then your second path is to formally identify the attacker with a Cyber investigation techniques and then take one of a few tactics at that point. While not nearly as expensive as litigation, this will still cost in the low 1’000s of dollars to implement.

If you want to bear the consequences and looking for a Defamation Expert then I would recommend you to visit http://www.cyberinvestigationservices.com/our-services/internet-defamation/ more than likely, they will be able to help.