This is the eighth such week-long operation, which this year unfolded in 106 cities. The FBI says nearly 3,600 children have so far been recovered from the street.
"I hate that we have to do this work hate it," Comey said. "I love the people who've devoted their lives to doing this work. There is no more meaningful work that the FBI participates in than rescuing children."
He said the operations were designed to "crush these pimps" and show that children are not for sale. They are also intended to rescue children who are being trafficked on street corners, in truck stops and, increasingly, on the Internet, where pimps advertise and arrange sexual encounters.
One challenge, officials said, is that many of the children who were recovered were never reported missing in the first place by parents, guardians and the entire child welfare system designed to protect them.
"No one is reporting them missing. Hence, no one is looking for them," said John Ryan, CEO of the National Center for Missing and Exploited Children. "But for operations like this, these children likely would never have been found."
He said better laws were needed to require child welfare service to report children who disappear. Right now, he said, only two states have laws requiring agencies to report children missing from their care. There is no national, uniform standard.
"We cannot find them if no one reports them missing," Ryan said.
Though this operation is the FBI's eighth of its kind, Comey said this year featured the highest number of participating cities. But he said the biggest change was the increasing prevalence of children being sold online rather than on street corners.