Stop presuming this man is a kidnapper.

Playing online detective can be a dangerous game.

You may have seen this photo circulating on social media in recent days.

According to a man in New Delhi, this stranger on a train is a human trafficker.

This assumption is based on the fact he is an Indian man holding a white child. He also assumes that the child is sleeping because it has been drugged. He asks punters to share the post and get this (maybe) stolen boy back to his parents (if he is not in fact already asleep on his father’s lap).

It is circulated. And widely.

Posted on Facebook only a couple of days ago, the picture has already been shared more than 400,000 times.

Now, according to online amateur sleuths, the boy closely resembles William Tyrell — the three-year-old boy who went missing from New South Wales’ mid-north coast last September.

No doubt NSW – who have a complex operation to find William in place – have since been inundated with phone calls.

While it’s heartening that people care and want to help find William Tryell, it’s concerning that, should the small white boy actually just be travelling with his relative or carer, the reputation of the man on the train has been internationally smeared.

For all we know, he could be a loving father, now falsely labelled a child trafficker.

It wouldn’t be the first time online vigilantes have got it wrong.

Related: Man takes a selfie. Next minute, he is the victim of an online hate campaign.

Last month, a Victorian woman posted a photo of a “creep” in a shopping centre who she claimed was taking photos of children.

WRONG.

Turns out he was just a daggy dad taking a selfie out the front of a Darth Vader display to send to his own teenage kids.

The woman posted a rant with the picture that included these words: “Hopefully he is a registered sex offender and he will be charged.”

The post was shared so widely that the man’s partner eventually saw it. The man was abused on his way to the police station to clear up the misunderstanding.

Also in May, a South Australian man suffering from dementia was assaulted, likely (police believe) as a result of a post shared on social media.

Someone uploaded pictures of the man because he was acting strangely by pulling faces at people and trying to engage them in conversation.

WRONG AGAIN.

While the enthusiasm of the well-intentioned social media vigilante is admirable, playing detective online is a dangerous game.

Especially, without any detective training or skills.

For a far more serious example of the online vigilante mob wrongly accusing someone of a horrific crime from the comfort of their own homes, we need look no further than the Boston Marathon bombing in 2013.

Related: Boston bomber Dzhokhar Tsarnaev sentenced to death.

When photos of the suspects began to circulate, a Reddit user posted side-by-side images of the then unidentified bomber and missing (now deceased) 22-year-old Brown University student, Sunil Tripathi, speculating that they were one and the same. The haphazard detective work sparked an internet snowball that resulted in reporters and public figures like pop-culture blogger Perez Hilton tweeting the speculative theory to millions. In the midst of a national manhunt for the culprits, many were giving premature credit to the Reddit community for solving the crime.

WRONG.

Tripathi’s family say the false identification of their son as one of the bombers derailed their search for him and added further and unnecessary trauma to their lives.

The reputations of innocent people are being smeared by sloppy fact-finding by rash and reckless sleuths keen to name and shame, flinging the floodgates for defamation law suits wide open.

With the extra powers for searches, surveillance and access to information granted to investigative authorities (not to mention the benefit of training and experience), they’re in a far better position to solve crimes than an amateur gumshoe with a broadband connection.

As for the image of the man on the train currently floating around cyberspace, police are looking into it.

NSW Police spokesman Rory O’Connor told Mamamia the Facebook image was one of the 100-plus possible sightings of William Tyrell reported to police since the boy went missing.

He urged anyone with information to contact police via Crimestoppers on 1800 333 000.

By all means, we should be vigilant. We should take notes and photos of suspect things. We just need to share our suspicions with the right type of detective.

For more on the William Tyrell case, try these articles:

The parents of William Tyrell have a heartbreaking message: “Just give him back.”

William Tyrell investigation: When guilt is (unfairly) presumed instead of innocence.

William Tyrell’s parents have written a heartfelt plea for help.

Are you opposed to online vigilantes?