In almost every major city in the United States, advocates say victims of human slavery are exploited everyday.
"Human trafficking is a very serious problem in the United States," says Bradley Myles of the Polaris Project, an organization that fights human trafficking.
According to Myles, some of the victims are forced to work in the homes of the wealthy and at restaurants. Many others, especially women, are forced into prostitution.
"We know from our very own eyes that it's happening. We're not kind of hearing it third hand. We've been inside those places. We work with those women."
The Polaris Project operates a human trafficking hotline. Calls come in from around the country.
"So we're getting calls from Texas. We're getting calls from California. We're getting calls from New York, Florida and DC is one of those top five cities where we're getting calls," says Myles.
Deborah Sigmund, founder of the advocacy group, Innocents at Risk, says most of the victims of human trafficking come from economically depressed countries and are lured to the U.S. with promises of a better life.
"They want to think that they can come to America and have a great job so it's very easy to fool them," she says.
According to the experts, some of the victims are forced to sell sex from brothels disguised as massage parlors.
Tim Whittman of the Federal Bureau of Investigation is an expert on human trafficking in the U.S.
"The number one foreign country is Mexico," says Tim Whittman, an expert on human trafficking with the U.S. Federal Bureau of Investigation (FBI). "Approximately 20 percent of our cases involve victims from Mexico."
The nation's capital is not immune to the problem. In Washington, the Polaris Project sees sex trafficking victims who are U.S. citizens, and women from South Korea, China and Latin America.
While some of their clients are middle class professionals from the community at large, many brothels will only accept a narrow clientele to make it difficult for law enforcement to catch them.
"If a person for example from Korea is brought in to the United States under false pretenses and then forced into prostitution very much that place where the prostitution occurs is within the Korean community in the United States," says the FBI's Whittman.
A study by The Human Smuggling and Trafficking Center finds nearly 83 percent of suspected human trafficking incidents involve sex trafficking. Advocates say other types of human slavery include people being forced to work as domestic servants and in agriculture. The FBI says the smugglers often threaten their victims and make it difficult for them to pay off their debts.
"Commonly, it's a threat against their family back in their home country and it's used to put that person in a position where they feel compelled to provide labor or service in the United States," says Whitman. "A common threat is if you leave we're going to report you to immigration and you'll be arrested, you'll be kept in prison for a long time."
In reality, there is help. Victims of human trafficking can sometimes be granted a special visa that allows them to stay in the U.S. for up to four years. During that time, they may apply for permanent residency.
But with threats, a language barrier and fear of the legal system, victims often do not or are unable to seek help.