The Mexican drug cartels have expanded into the flesh trade as reported by Ioan Grillo for Time Magazine: "activists estimate that hundreds of thousands of women in Mexico, including many underage girls, are coerced into sex work or other forced labor," and "in addition to selling women for sex, Mexican cartels also have been known to kidnap women and girls and use them as their personal sex slaves."
Child sex once was considered among the lowest crimes even within underworld circles but in recent years it's become a racket staple for the most powerful crime groups and street gangs.
For example, in Northern Virginia 12 MS-13 gang members "have been locked up for child sex trafficking in the past two years" as reported by Pamela Brown for WJLA:
"We're seeing most of the cases coming from MS-13 with regards to sex trafficking and we've seen a number of those cases from the past year," said John Torres, Special Agent in Charge with ICE Homeland Security Investigations. "For us it's a disturbing trend."
In August 2011 the Chicago Police Department arrested nine individuals for their alleged roles in a "'major' human sex trafficking operation run by Vice Lords and other gang members on the South and West Sides" as reported by Rummana Hussain and Mitch Dudek for the Chicago Sun-Times: "some of the victims were as young as 12 when they were recruited to work as prostitutes."
A major child prostitution ring allegedly run by the Oceanside Crips in North County, CA was busted in April 2011 as reported by Lindsay Hood for NBC:
During the investigation, detectives found 30 female minors who claimed they were being held by the gangs against their will. * * * The gang members would target runaways or girls from broken homes. Investigators allege the gang members would often gift the women and girls to each other. The prostitutes would be punished through physical violence if they disobeyed their pimps.
In October 2010 the feds indicted 29 men and women for their alleged roles in decade-long interstate child sex trafficking operation run by Minneapolis, MN-based Somalian street gangs which forced girls as young as twelve into prostitution as reported by the Star Tribune.
California Assemblyman Marty Block said street gang members "are recruiting teenage girls for prostitution in schools and 'selling them over and over'" as reported by KPBS: "Where drugs can only be sold once, girls are a 'renewable resource for gangs,' he said."
Sex trafficking in women and children is the second biggest racket -- behind drugs -- for organized crime and street gangs in the United States which provides annual revenue of $9 billion, and the FBI estimates more than 100 criminal groups have their dirty hands in the illicit trade which use strips clubs, massage parlors and Craigslist and other web sites to peddle their product.
Further reading that may be of interest: