New York (CNN) Terrifying rumors initially propelled by Facebook's algorithms have sparked fears that men driving white vans are kidnapping women all across the United States for sex trafficking and to sell their body parts. While there is no evidence to suggest this is happening, much less on a national, coordinated scale, a series of viral Facebook ( FB ) posts created a domino effect that led to the mayor of a major American city issuing a warning based on the unsubstantiated claims.

The latest online-induced panic shows how viral Facebook posts can stoke paranoia and make people believe that spotting something as common as a white van, can be deemed suspicious and connected to a nationwide cabal.

"Don't park near a white van," Baltimore Mayor Bernard "Jack" Young said in a TV interview on Monday . "Make sure you keep your cellphone in case somebody tries to abduct you."

The mayor said he had not been told of the apparent threat by Baltimore Police but said it was "all over Facebook."

Matthew Jablow, a spokesperson for the Baltimore Police Department, told CNN Business on Tuesday that while the department is aware of posts on social media it had not received "any reports of actual incidents."

Indeed, while there is no hard evidence of any such phenomenon in Baltimore, unconfirmed reports of suspicious white vans in Baltimore and other cities across the US have been shared hundreds of thousands of times on Facebook in recent weeks and have been seen by potentially millions of Facebook users. At least one person who drives a white van has reported being harassed for it as a result of the rumors.

Baltimore City Councilman Kristerfer Burnett, co-chair of the Baltimore City Human Trafficking Collaborative , told CNN Business that he worried that the panic about white vans would distract from the wider issue of human trafficking.

"We need to make sure accurate information is out there especially because Baltimore is a hotbed of human trafficking in the country," Burnett added.

He said the rumors had spread mostly through Facebook, "which I think is sort of telling given the national conversation around Facebook's ability and inability to control the spread of inaccurate information on their platform."

In Georgia, police investigating reports of suspicious white vans have asked the public to call 911 rather than post on social media.

Going viral

Sightings of "suspicious" white vans in Baltimore have been reported on Facebook for years. For example, CNN Business found one 2016 post from a woman who warned there was a white van outside her home and that people should be careful because there was "a guy in a white van kidnapping kids."

Contacted by CNN Business Tuesday, the woman said she had no specific evidence to back up the claim but that she had heard it "plenty of times" and was only trying to warn her friends who have children.

While that posting barely received any attention, there has been a flurry of posts about white vans in Baltimore over the past month that have gone viral on Facebook and Instagram, which is also owned by Facebook.

On November 13th, Saundra Murray, a Baltimore resident, posted photos of a white van outside a gas station to Instagram. Murray said two men in the van would not stop staring at her while they were in the store. Murray told CNN Business she had seen the men in the store before she knew they were in a white van. She said she didn't report the incident to police "because I didn't have much information to report but I did want to make the [Instagram] post to let people know what is going on."

Murray said she had seen reports on social media of suspicious white vans but she thought people were exaggerating -- mysterious white vans are a "big thing in movies," she thought, and believed that might have added to the exaggeration.

However, after her experience, she now believes the men and the van are "part of a bigger story, I don't think they are two random guys."

Baltimore Police has received no reports of actual incidents.

Murray's post racked up more than 3,200 likes on Instagram. A few days later, on November 17, another woman in Baltimore posted screenshots of Murray's Instagram post to Facebook. That Facebook post had been shared more than 2,000 times by this Tuesday.

A separate Facebook post from another woman in Baltimore on November 18 that was shared more than 5,000 times showed a stock image of a white van and warned: "When you come out into the mall parking lot, and you see a van like this parked next to your car, DO NOT GO TO YOUR CAR."

The post claimed that sex traffickers had "these vans rigged where they lock from the outside, and, once inside, you can't get out."

But the posts were not only going viral in Baltimore. A Facebook post from a man in South Carolina on November 15 showed a photo of a white van with two external locks. The photo appeared to have been taken from Snapchat.

"IF U SEE ANY VANS LIKE THIS CALL 911 THIS IS UTILIZED FOR SEX TRAFFICKING," the Facebook post read.

The post was shared an extraordinary 151,000 times.

Beyond Facebook

To help tackle its misinformation problem, Facebook has hired third-party fact-checkers. On November 21, one of the company's partners, Lead Stories, ran a fact-check that said people don't need to be particularly concerned just because they spot a van with external locks.

Lead Stories pointed out that external locks on vans are commonly used by construction workers who keep expensive tools in their vehicles.

The fact-check has been applied to some Facebook posts about white vans, meaning Facebook users who try to view those posts will be alerted that the information is false.

But while that might help slow or stop the spread of such posts in the future, it can't undo the damage done or prevent the information from going elsewhere. On Tuesday, screenshots of the Facebook post were circulating through an email listserv for parents in a New York suburb, CNN Business learned.