In a published decision, the Eleventh Circuit declined to recognize former members of the Mara 18 as a particular social group. In so doing, the court relied heavily on published Board of Immigration Appeals (BIA) and Ninth Circuit case law finding that - for policy reasons - it would be inappropriate to reward applicants with immigration status based on prior, anti-social and violent behavior. The court also deferred to the BIA's determination that a group comprised of former gang members lacked sufficient particularity.
The full text of Gonzalez v. Attorney General can be found here: http://media.ca11.uscourts.gov/opinions/pub/files/201512878.pdf