Agents arrested more than 150 people on sex-trafficking charges in dozens of cities including Atlanta, Denver and Seattle.
The youngest victim found was 12 years old, the FBI said.
The FBI targeted hotels, casinos and lorry stops to find underage victims.
The majority of the teens found were girls. Agents also found three boys and three transgender teens.
The FBI worked with local police departments and the National Center for Missing and Exploited Children to help the teenage victims to find shelter and get medical attention.
The agencies want to ensure the teenagers do not return to prostitution.
"When kids are treated as a commodity in seedy hotels and on dark roadsides, we must rescue them from their nightmare and severely punish those responsible for that horror," FBI Director James Comey said in a statement.
The raids involved about 500 local police departments from across the country. A similar FBI-led campaign carried out last year uncovered about 160 teenagers working as prostitutes.

Unite union members based at plants in Cowley, Goodwood, near Chichester, Hams Hall in the West Midlands and Swindon, turned down the offer by 56.6%.
Workers have already staged four walkouts during the dispute, which is over the closure of a final-salary pension scheme.
BMW said the offer was "fair" and it was disappointed at the ballot result.
Unite representatives will meet on Tuesday to discuss the next steps in the dispute, which has seen the first-ever strikes by the company's British employees.
Three 24-hour strikes scheduled in May were suspended while workers considered the offer, which the union did not recommend to its members.
Unite national officer Fred Hanna said: "It is clear that it did not go far enough or deal with the concerns many of our members have over BMW's pension plans.
"We would urge BMW bosses to reflect on the result and listen to the workforce by further engaging in meaningful talks with Unite."
A BMW spokesman said: "We are now considering the implications of the ballot result and we will be meeting with the union in due course to discuss next steps.
"We believe the offer, which resulted from lengthy negotiations with the union since September last year, was fair.
"It was designed to improve competitiveness, which is in the long-term interests of all our employees in the future."
The FBI has broken up several sex trafficking rings across the US, uncovering more than 100 sexually exploited teenagers in a nationwide operation.
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Workers at car giant BMW have voted to reject an offer aimed at resolving a long-running dispute over pensions.