NEW YORK (THOMSON REUTERS FOUNDATION) - A teenage girl who claims she was forced to have sex with men for two years from the age of 14 is suing a roadside US motel in a landmark case, accusing the business of turning a blind eye while she was sex-trafficked.

It is the first case brought under a 2014 law in the state of Pennsylvania that allows victims to sue those who profit indirectly from their trafficking.

The teenager, identified as MB in the complaint, was held captive in budget motel the Roosevelt Inn in Philadelphia from as young as 14 and forced to have sex with men several times a day for more than two years, the complaint said.

The civil complaint is the first filed under Pennsylvania's Human Trafficking Law which expands the definition of the crime and allows civil proceedings against those who participate or profit from it, said Shea Rhodes, director of the Villanova Law Institute to Address Commercial Sexual Exploitation.

The milestone case is likely to encourage attorneys and victims to make use of the law again in future cases, she said.

"Putting motels or other industries that facilitate trafficking on their premises (on notice), holding them civilly accountable, will discourage additional hotels or motels from allowing this insidious crime to happen on their premises," said Rhodes in a phone interview.

When the Roosevelt Inn was contacted for comment by phone, a receptionist said management had nothing to say.

According to the suit that was filed on Friday, Roosevelt Inn staff regularly leased rooms to the teenage girl's traffickers from 2013 despite knowing their actions were facilitating her sexual exploitation.

The complaint alleges one motel clerk in particular "was fully aware" that the victim was a minor and would direct clients to the room where MB was held.

"Once in the hotel, she was forced to stay there for days, sometimes longer than that. Not permitted to go far beyond the room that she was in, and was not allowed to leave the motel,"said Nadeem Bezar, an attorney for the teenager in a phone interview.

The victim's traffickers were convicted in a separate criminal case and are currently serving jail time, Bezar told the Thomson Reuters Foundation.

The teenage girl is seeking financial compensation in excess of US$50,000 (S$70,000).

Most US states allow for businesses profiting from human trafficking to be the subject of lawsuits, but Pennsylvania has enacted the most robust law, said Rhodes.

She said there may have been less than half a dozen such cases involving hotels, partly because of the danger of retraumatising victims by involving them in an additional lawsuit after having already been through criminal proceedings.

Over the past decade, anti-slavery group Polaris said it had received reports of more than 22,000 sex trafficking cases in the United States.

Globally, nearly 21 million people are victims of human trafficking, according to the UN's International Labour Organisation. An estimated 4.5 million are forced into sex work.