I think that each individual should report their incident at this link..
http://www.uspsoig.gov/investigation.htm (look at the "Quick Links" to the right of the page and click "Report Fraud")
I would think that several reports about the same person or to the same mailing address would get more attention than one report with every ones name attached. Also if they were able to determine that any type of crime was committed each person would have a case number to their specific incident.