Story highlights The Bay area and Detroit have the most arrests and child rescues

The FBI says the three-day undercover operation is its biggest to date

105 children across the country are rescued in the nationwide operation

The ages of the children involved range from 13 to 17

They are mostly teenage girls, often from broken homes where no one misses them. Their world is one of drugs and abuse -- emotional and physical -- in which they are forced to sell their bodies.

In announcing the FBI's latest crackdown on child prostitution, officials Monday described a dark underside of society that has grown through Internet sites that provide pimps easy access to johns in hotels, motels, at truck stops and just about anywhere else.

The nationwide operation over the weekend resulted in 150 arrests, with 105 children between the ages of 13 and 17 rescued, according to Ron Hosko, assistant director of the FBI's Criminal Investigative Division.

Overall, the three-day undercover Operation Cross Country took place in 76 cities and involved 230 law enforcement units, Hosko told a news conference.

It was the largest such sweep to date, he said, with 28 searches and 129 seizures of cash, drugs, vehicles and firearms. Those arrested face a variety of federal and state charges, including pimping.

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This seventh iteration of Operation Cross Country also was the most successful, with a 30% to 40% increase in "identifying both victims and pimps" compared with previous operations, Hosko said.

He credited the success in part to an expansion of the probe to websites such as www.backpage.com, which he called a forum "where pimps and exploiters gather."

Authorities also have learned more about how the market thrives. For example, Hosko explained that major sporting events such as the Super Bowl and the NCAA Final Four attract tens of thousands of visitors with money who want to party, and pimps with prostitutes ready to cash in.

"We have had children recovered from each of those events, multiple children from each of those events in the past," he said.

While technology has changes methods of procurement, the underlying demographics of the child victims of the prostitution industry remain little changed -- young girls around 13 to 16 years old with few or no family ties.

"That tends to be the age that many of us as loving and caring parents occasionally find some differences with our teenage daughters, and exploiters will exploit that gap," Hosko said.

A breakdown of cities where the latest arrests took place, and where child prostitutes were recovered, reveals some unexpected findings.

The San Francisco-Oakland region in California had 17 arrests and 12 recovered child prostitutes, while Detroit, which just declared itself bankrupt, had 18 arrests and 10 rescued children.

Meanwhile, New York City had none of either, Las Vegas had one of each and New Orleans had five arrests and four recovered children, compared with 13 arrests and three child prostitute rescues in Oklahoma City.

"This operation serves as a reminder that these abhorrent crimes can happen anywhere," Hosko said.

Operation Cross Country is part of the FBI's Innocence Lost National Initiative, which seeks to identify children lured or forced into prostitution and remove them from risk, according to Hosko.

The circumstances of the situation make finding victims especially difficult, he explained.

"Commonly some of these children have stepped away from their families," he said, adding that "there is no one to call and report 'my daughter is missing.'"

Other major problems are the culture of abuse, both physical and emotional, and the drug use prevalent in child prostitution.

"We have victims whose new normal is abuse and is drug-infected," Hosko said, explaining there is an environment of instability in which "the expectation of somebody who cares about them may last for 30 minutes or an hour before the abuse starts again."