The tip-off came within hours of the boy's image being posted on Facebook.
Grace Barnes, 28, was contacted by a childhood friend who had shown the CCTV footage to her cousin, who in turn had shown it to her young daughter.
The girl said she recognised the boy carrying off a dog in the grainy video as a classmate at her eastern suburbs high school.
Barnes, a naturopath from Bondi, thought the social media campaign to track down her Staffordshire bull terrier Buckie had yielded results.
Police were called in. The boy's mother and school were brought into their investigation.
The only problem: he was not the boy in the video.
It is perhaps lucky that officers were first to interview the suspect, and able to confirm the error.
The fate awaiting the as-yet unidentified boy in the video could be worse. Among the 8000 people to have visited the Help Us Find Buckie Facebook page, some describe the boy - who has not been identified, let alone charged or found guilty of any crime - as a "mongrel", "little shit" and worse. He should be castrated, assaulted, burned alive, some say. "Kill the kid kill the parents and the entire family!!," writes one.
Another Facebook user has posted a photo of a Sydney boys' soccer squad and suggested the likely culprit is among them.
The story of missing Buckie is just one example of a growing trend of cyber sleuths setting out to solve crimes through social media.
Sometimes - such as in the case of a break-in at the Annandale Hotel - their efforts can yield results.
But such pursuits can also be far from passive or peaceful - prompting NSW Attorney-General Greg Smith to warn of the potential to "create a sense of vigilantism in the community".
The threat of violence through an act of cyber vigilantism is real and growing, legal experts say. This week, the hacktivist group Anonymous named a "cyber bully" it says drove Canadian teen Amanda Todd to suicide, prompting online hate pages calling for his death - despite his identity remaining unconfirmed.
An English court heard this month how a man used social media to track and attack a man who allegedly raped his wife as a schoolgirl.
Similarly, a 52-year-old baseball umpire in New Jersey last year bashed a man he mistakenly thought had stolen his iPhone - after believing he had tracked the culprit using a smartphone application.
For her part, Barnes has sought to remove offensive postings from her Facebook page among the hundreds of messages expressing only sympathy for her plight.
"We have no intention of hurting this kid in any way. We just want to get the dog back," she says.
But once she put his image online it was out of her control.
"By putting stuff online you are basically saying 'If it feels good, go out and lynch someone,'" says David Vaile, executive director of the Cyberspace Law and Policy Centre at the University of NSW.
"It's a reversion back to the era when someone is supposed to have the right to be judge, jury and executioner. There is no quality control or qualifications required in terms of commonsense or decency or fairness or capacity to show any of the restraint required of the legal system."
Smith supported the setting up of a working group of attorneys general to look at legal issues arising out of social media, along with cyber bullying.
"Educating users of social media about the responsible use of the medium and making them aware of the possible impact of their comments is one important element of the new working group. Developing protocols for the quick removal of offending materials is another," he says.
Solicitor Stuart Gibson recently issued defamation proceedings in the Supreme Court after a client was erroneously identified on Facebook as a "sexual miscreant". Cases of people being mistakenly identified online as criminals, either mischievously or through error, are increasing, he says.
Gibson also acted for music reviewer Joshua Meggitt when he was mistakenly identified by columnist Marieke Hardy on Twitter as being the author of a hate blog. Hardy subsequently apologised to Meggitt and paid him a confidential settlement that was "considerably higher" than the $15,000 reported, Gibson says. "It was a grotesque way to be portrayed and it had a very big impact on him and his family.
"An online vigilante mentality ensued in which many online non de plumes attacked him and me."
NSW deputy privacy commissioner John McAteer is concerned by the growing trend of people using social media and CCTV footage to hunt alleged criminals.
"Law enforcement is a matter for law enforcement bodies and members of the public shouldn't be taking matters into their own hands," he says.
He is particularly critical of images of children being posted online in connection with an alleged crime, without the consent of their parent or guardian.
Sydney media law barrister Mark Polden was involved in a custody dispute in which images of children were put online by one party in connection with making untrue allegations about the other parent.
"That resulted in an attempt to run somebody over by another person in a car," he says.
"Members of the extended family and other people in the local area had seen the allegations on the website and assumed they were true and, as a result, that person was attacked."
Not all cases of cyber sleuthing are malicious, Polden points out. Security camera images of Melbourne woman Jill Meagher helped inspire large-scale concern for her whereabouts, then collective grief when her body was found last month.
CCTV footage showing Meagher walking on Sydney Road, Brunswick, on the morning she disappeared was shared on social media about 7500 times within two hours.
But when a man was charged with her rape and murder, some of those mourners started Facebook hate pages inciting violence and sharing details of the man's background. Victoria Police have warned such postings could prejudice a jury trial and pressured Facebook to remove the pages this month.
Pictures of the alleged killer of Thomas Kelly, who died after being king-hit in Kings Cross in July, were similarly plastered over Facebook and Twitter, with accusations of "monster" and "murderer". "Anyone can understand how upset people become when anything like that happens but how quickly that can turn into something which puts any fair trial of the accused person at risk," Polden says, in relation to the Meagher case.
"It is important to remember accused people have rights too and people do make mistakes in identifying people. In those circumstances to then put material up is not only to incite vigilante justice ... but is counter-productive because anyone who has seen the material may be called up to jury duty."
What prompts someone to threaten to shoot a child over a missing dog? Kristen Boschma, head of digital and social media at communications firm Haystac, says such online comments are typically driven by a desire to be controversial rather than genuine malice.
Online users are increasingly learning how to harness the power of social media, she says.
"Cyber vigilantism applies to the higher end of the scale and implies people will take the law and other people's safety into their own hands, often with aggressive and dangerous consequences," she says.
"Then there is the more mid-level scale where people add their voice to a cause online or join a petition or comment on a particular brand's Facebook page ... I would say that behaviour is a new form of collective protest but it's not cyber vigilantism."
Grace Barnes's sad tale of her "stolen" dog has featured in newspapers and on television and radio.
"Someone's always watching, that's the thing to remember. You can't get away with anything these days," she says.
But for the moment, at least, no one has seen Buckie - or is willing to say so. Police are continuing to investigate. Barnes offered a $1000 reward for the return of her pup, who was never one to stray.
Perhaps to inspire charity rather than condemnation on Facebook, her most recent post implored people to carry out a random act of kindness, "safe in the knowledge that one day someone might do the same for you".
- Sydney Morning Herald