“Any info on Chris* please? Thanks.” The words in a Facebook post, above three pictures of a man. In the comments, a woman replies: “He was also posted a few days ago by someone.”

Further down, a second woman replies: “I’m shaking, I’m his fiancee.”

Interactions like this happen almost daily in the vast network of “Are We Dating The Same Guy?” Facebook groups that now span the globe.

Open only to women, who must pass vetting checks to be admitted – administrators will root out new profiles, and decline any that look fake – they are designed to share information about men.

A group for New York City has 164,000 members, the Los Angeles group has 79,000, one for Toronto has 81,000, and Sydney 10,000.

In the UK, there are groups for every region and nation, from more than 150,000 women in a group for Londoners, to 2,500 members in a page for the Lancashire towns of Blackburn and Darwen. There is even a specific group for UK women with partners in prison, with more than 800 members.

While designed to catch cheaters, they are also acting as a resource to warn women about violent, abusive and dangerous men.

“The Are We Dating the Same Guy? Facebook groups had helped thousands of women around the world avoid cheaters, narcissists and abusers,” one UK-based member said.

“The times of men being able to have second families and serially abuse women with abandon are over. In my personal experience, I don’t even have Facebook, but a month ago I was looking at the group on my friend’s phone only to find out a man I had been talking to had killed someone and was in jail for manslaughter.”

Another woman said her sister had posted in the groups, feeling that something was off when a man ghosted her after telling her his donkey had died. She found out from Facebook that he didn’t have a donkey, but he did have a fiancee.

“I think that spaces like these where women can share stories that could possibly lead to someone saving themselves from a dangerous situation with a person are absolutely necessary,” she said.

“I think they’re a good tool for warning women away from cheaters or abusers – I’ve seen a lot of that in my local group,” said another woman, based in the US.

“But a lot of the times the posts, [or] who comments, get back to the guy. Somebody shared what I said with my ex; he’s not a bad person so it wasn’t a concern, but I can imagine that potentially being dangerous when people don’t respect the privacy rules.”

“A lot of the abuse that gets referenced is more emotional abuse [or] narcissistic tendencies from what I’ve seen – stuff that’s not necessarily illegal but still detrimental,” she added. “So in instances like that, sometimes women’s best resources are each other, and I’ve seen a lot of encouragement and support in the group, too.”

In the UK, under the Domestic Violence Disclosure Scheme (DVDS), known as Clare’s law, police forces are able to disclose information about a perpetrator’s previous abusive or violent offending to a victim or potential victim of domestic abuse.

Under the scheme, it is possible to ask the police to check whether a current or ex-partner has a violent or abusive past – and the topic is raised regularly in the groups, with, in some cases, women finding out about their partners’ criminal histories through tipoffs on Facebook.

However, some experts say the groups are not without risk, and may even put women in danger of further harm.

“The Are We Dating the Same Guy? Facebook groups highlight both the necessity and the limitations of women turning to online communities for protection,” said Charlotte Proudman, a family law barrister.

“Given that one in four women will be raped or sexually assaulted, and many lack confidence that statutory services will keep them safe, it is understandable that women are using these spaces to share red flags and warn each other about dangerous men.

“However, there are risks, including the possibility of violent men retaliating if they discover they have been named, or women facing legal threats for speaking out.”

“There is a defamation risk,” said Mark Stephens of Howard Kennedy LLP, “and one of the challenges, particularly of abusive and controlling men, is that they are increasingly using defamation laws to silence women about their abuse.”

Even posting anonymously – which many of the groups allow – would not necessarily offer protection, he said.

“For ordinary blokes, it’s not going to be too much of a risk, because they won’t have the money,” he said, “but for rich and powerful men, what we’re seeing increasingly is that they will apply to Facebook, Meta, and ask for details of the person who posted, so they can launch legal proceedings against them, and they get a court order from the court to disclose the woman’s details.”

Some who work in the sector have said that the fact that the groups exist at all is an indictment on the failures of the state to keep women safe – leaving women themselves to fill a vacuum created by statutory services.

“One of the things that stands out for me, working with women who have been subjected to men’s violence, is how women have each other’s backs,” said Karen Ingala Smith, the chief executive of nia, a domestic and sexual violence charity. “I am so pleased to see that women are using technology to adapt and advance sisterhood.”

One of the issues with Clare’s law, she said, was that even where it crossed the threshold of criminality, men’s violence against women was rarely reported.

“Using the police and courts to address abusive men is a step that many women choose not to take and for many good reasons,” she said.

“And while I wish that abusive men were fully and formally held to account for their actions, in this world with a very far from perfect, or even adequately functioning, justice system, when it comes to men’s violence against women, I am delighted that women find other ways to protect each other. Sisters are doing it for themselves. Long may it continue.”

*Names have been changed.