Isn't he in jail now? And also, which individuals? We are lucky enough to live in a society where "expressing concern" is not sufficient to put someone in jail.
Yes he is in jail, read the Wikipedia article for the details but basically people reported concerns to the SEC on 5 separate occasions beginning in 1999. The SEC ignored the complaints until Madof himself admitted to his sons in 2008 that it was a total ponzi and his own sons turned him in to the FBI. After he was arrested by the FBI in 2008 the SEC aka "the regulator" took action against him in 2009. Point is the regulator in charge didn't bother to investigate and didn't do anything.