As for websites, Liz McDougall, the general counsel for Backpage.com, said that if that site were shut down to the advertisements in question, the information that can lead to the rescues would be lost to law enforcement because the ads would be pushed to "offshore uncooperative websites."
"We feel very strongly that we're doing the right thing, and we're going to continue to do the right thing and we congratulate the FBI and everybody with the task forces involved in the program," said McDougall.
In earlier sweeps, child prostitution victims have been recovered at major sporting events — including the NCAA Final Four and Super Bowl, Hosko said.
In the 1990s, gangs took control of street prostitution across America; that forced pimps to move girls into sporting events where security existed, said Dr. Lois Lee, founder and president of Children of the Night, a nonprofit group that has rescued 10,000 children from prostitution since 1979.
Hosko said the plight of the young people often goes unreported to authorities because the children in many instances are alienated from their families and are no longer in touch.
In Oakland, Calif., police Lt. Kevin Wiley said authorities are "always afraid" for the girls.
"They usually get into this because they are running away from something else," said Wiley. "You're trying to find out what brought them into this lifestyle in the first place. It goes way beyond law enforcement to solve this epidemic."
Pimps operate wherever vulnerable potential victims can be found. Some are being recruited right out of foster care facilities, Hosko said.
For the past decade, the FBI has been attacking the problem in partnership with a private group, the National Center for Missing and Exploited Children.
John Ryan, the head of the center, called the problem "an escalating threat against America's children."
The Justice Department has estimated that nearly 450,000 children run away from home each year and that one-third of teens living on the street will be lured toward prostitution within 48 hours of leaving home.
Congress has introduced legislation that would require state law enforcement, foster care and child welfare programs to identify children lured into sex trafficking as victims of abuse and neglect eligible for protections and services.
"In much of the country today, if a girl is found in the custody of a so-called pimp she is not considered to be a victim of abuse, and that's just wrong and defies common sense," Sen. Ron Wyden, D-Ore., said during a Senate Finance Committee hearing last month. Wyden co-sponsored the legislation with Sen. Rob Portman, R-Ohio.
Associated Press writer Lisa Leff in San Francisco contributed to this report.