By NICHOLAS D. KRISTOF

I WENT on a walk in Manhattan the other day with a young woman who once had to work these streets, hired out by eight pimps while she was just 16 and 17. She pointed out a McDonald’s where pimps sit while monitoring the girls outside, and a building where she had repeatedly been ordered online as if she were a pizza.

Alissa, her street name, escaped that life and is now a 24-year-old college senior planning to become a lawyer — but she will always have a scar on her cheek where a pimp gouged her with a potato peeler as a warning not to escape. “Like cattle owners brand their cattle,” she said, fingering her cheek, “he wanted to brand me in a way that I would never forget.”

After Alissa testified against her pimps, six of them went to prison for up to 25 years. Yet these days, she reserves her greatest anger not at pimps but at companies that enable them. She is particularly scathing about Backpage.com, a classified advertising Web site that is used to sell auto parts, furniture, boats — and girls. Alissa says pimps routinely peddled her on Backpage.

“You can’t buy a child at Wal-Mart, can you?” she asked me. “No, but you can go to Backpage and buy me on Backpage.”

Backpage accounts for about 70 percent of prostitution advertising among five Web sites that carry such ads in the United States, earning more than $22 million annually from prostitution ads, according to AIM Group, a media research and consulting company. It is now the premier Web site for human trafficking in the United States, according to the National Association of Attorneys General. And it’s not a fly-by-night operation. Backpage is owned by Village Voice Media, which also owns the estimable Village Voice newspaper.

Attorneys general from 48 states have written a joint letter to Village Voice Media, pleading with it to get out of the flesh trade. An online petition at Change.org has gathered 94,000 signatures asking Village Voice Media to stop taking prostitution advertising. Instead, the company has used The Village Voice to mock its critics. Alissa thought about using her real name for this article but decided not to for fear that Village Voice would retaliate.

Court records and public officials back Alissa’s account, and there is plenty of evidence that under-age girls are marketed on Backpage. Arrests in such cases have been reported in at least 22 states.

Just this month, prosecutors in New York City filed charges in a case involving a gang that allegedly locked a 15-year-old Long Island girl in an empty house, drugged her, tied her up, raped her, and advertised her on Backpage. After a week of being sold for sex, prosecutors in Queens said, the girl escaped.

Liz McDougall, general counsel of Village Voice Media, told me that it is “shortsighted, ill-informed and counterproductive” to focus on Backpage when many other Web sites are also involved, particularly because Backpage tries to screen out ads for minors and reports possible trafficking cases to the authorities. McDougall denied that Backpage dominates the field and said that the Long Island girl was marketed on 13 other Web sites as well. But if street pimps go to jail for profiteering on under-age girls, should their media partners like Village Voice Media really get a pass?

Paradoxically, Village Voice began as an alternative newspaper to speak truth to power. It publishes some superb journalism. So it’s sad to see it accept business from pimps in the greediest and most depraved kind of exploitation.

True, many prostitution ads on Backpage are placed by adult women acting on their own without coercion; they’re not my concern. Other ads are placed by pimps: the Brooklyn district attorney’s office says that the great majority of the sex trafficking cases it prosecutes involve girls marketed on Backpage.

Alissa, who grew up in a troubled household in Boston, has a story that is fairly typical. She says that one night when she was 16 — and this matches the account she gave federal prosecutors — a young man approached her and told her she was attractive. She thought that he was a rapper, and she was flattered. He told her that he wanted her to be his girlfriend, she recalls wistfully.

Within a few weeks, he was prostituting her — even as she continued to study as a high school sophomore. Alissa didn’t run away partly because of a feeling that there was a romantic bond, partly because of Stockholm syndrome, and partly because of raw fear. She says violence was common if she tried connecting to the outside world or if she didn’t meet her daily quota for cash.

“He would get aggressive and strangle me and physically assault me and threaten to sell me to someone that was more violent than him, which he eventually did,” Alissa recalled. She said she was sold from one pimp to another several times, for roughly $10,000 each time.

She was sold to johns seven days a week, 365 days a year. After a couple of years, she fled, but a pimp tracked her down and — with the women he controlled — beat and stomped Alissa, breaking her jaw and several ribs, she said. That led her to cooperate with the police.

There are no simple solutions to end sex trafficking, but it would help to have public pressure on Village Voice Media to stop carrying prostitution advertising. The Film Forum has already announced that it will stop buying ads in The Village Voice. About 100 advertisers have dropped Rush Limbaugh’s radio show because of his demeaning remarks about women. Isn’t it infinitely more insulting to provide a forum for the sale of women and girls?

Let’s be honest: Backpage’s exit from prostitution advertising wouldn’t solve the problem, for smaller Web sites would take on some of the ads. But it would be a setback for pimps to lose a major online marketplace. When Craigslist stopped taking such ads in 2010, many did not migrate to new sites: online prostitution advertising plummeted by more than 50 percent, according to AIM Group.

Alissa, who now balances her college study with part-time work at a restaurant and at Fair Girls, an antitrafficking organization, deserves the last word. “For a Web site like Backpage to make $22 million off our backs,” she said, “it’s like going back to slave times.”