Cindy Choi’s long-running cancer deception underscores the dangers of predators on the ubiquitous Facebook social networking site, experts say.

Although Choi broke hearts and sometimes apparently stalked some girls, she never introduced herself physically. And no underage girls admitted to sexual activity over the phone or online.

Ultimately, prosecutors could not bring a case against Choi, who deleted her accounts and a blog before investigators could preserve them. If a user deletes a page, Facebook claims, the records are gone for good, although the company admits “some information may remain in backup copies or logs for up to 90 days.”

Her victims are calling for Facebook, which claims 1 billion users, to better ferret out fakes.

“I do think that Facebook is looking the other way because it benefits them monetarily and it benefits the number of users they can claim exists,” said Roger Masters, whose 19-year-old daughter fell in love with a young man created by Choi.

No U.S. law exists that requires Internet providers to retain records for a certain time period.

A spokesperson for Facebook did not respond to specific questions, instead directing a reporter to the site’s policy pages.

Across the nation, authorities have made many arrests of Facebook users who prey on young people or defraud the sympathetic.

Occasionally, the site provides police tips. In March, the site tipped off Florida Department of Law Enforcement agents that a 32-year-old Orlando man was seeking sex from a 13-year-old girl through the site. He was arrested.

In many more cases, perpetrators are caught after the fact.

In January 2010, a Key West man was arrested after authorities said he posed as a sorority sister on Facebook, blackmailing young women at Louisiana State University into posing nude.

Oscar Garcia, 30, was arrested in February after Miami police say he created a fake Facebook page to look at the page of a 11-year-old girl. He found a cell number on the girl’s page, offering to send her photos of his penis, police said.

In one extreme case, a British registered sex offender, posing as a teen in 2009, murdered a 17-year-old girl he met on Facebook.

As for cancer fakes, a New Jersey woman was arrested last month after investigators say she posed as a cancer patient, duping supporters into giving her more than $15,000. In September, an Arizona woman was jailed for one year after she falsely claimed to have breast cancer — using donations instead to pay for breast implants.

In a world that is so wired to the Internet, the Choi tale also serves as an example for parents to be more vigilant, said Jeffrey Cole, director of the University of Southern California’s Center for the Digital Future.

“The job of a parent has become so much more complicated in what they have to prepare their kids for,” Cole said.

He said of Internet hucksters: “Sadly, it’s not that uncommon. What seems to be extraordinary about this case is the context, the depth, the elaborateness of the deception. For most people, it doesn’t go back years and with this full cover story.”