According to the FBI's 2011 report called "National Gang Threat Assessment," Insane Clown Posse's followers, known as the Juggalos, are "a loosely-organized hybrid gang" with subsets that "exhibit gang-like behavior and engage in criminal activity and violence."
As Ackerman points out, the Juggalos are only identified as fans of Insane Clown Posse in a footnote.
According to the FBI, only four states recognize Juggalos as a gang, but 21 states have identified criminal Juggalo subsets. The Juggalos are particularly drawn to New Mexico, the reports says, because "they are attracted to the tribal and cultural traditions of the Native Americans residing nearby."
Juggalo crime is mostly disorganized and involves assault or drug use, but there have been some instances of more organized "gang-like criminal activity, such as felony assaults, thefts, robberies, and drug sales."
Here's a picture from the report, "Figure 6. Juggalo member":
Read the full report here.