A VIGILANTE commuter who boldly confronted train vandals and filmed them says they had to be taught a lesson.

The man, known only as Mark, said he was sick of seeing taxpayers' money wasted on cleaning up graffiti on trains before he boldly confronted the train vandals and filmed them, saying they had to be taught a lesson.

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So when he spotted three vandals tagging in a carriage as he was on his way home, he could not turn a blind eye.

"I thought, if these kids aren't taught now they'll probably think they will get away with it and continue doing it -- and probably end up in the big house when they are older. And you don't want that," he told Channel 9 News.

His footage shows him cornering two taggers as the third runs off.

"Guess what, matey? You're gone," he says.

"Guess where this is going, boys? Straight to Crime Stoppers."

The footage has gone viral, with more than 444,000 views on YouTube and 22,000 likes on Facebook in one day.

The video ends with Mark grabbing the two taggers, chasing them off the train at the next station, and trying to make a citizen's arrest.

Mark said he released one youth he was holding only after one of the boy's mates produced a rock.

Today, police spokeswoman Anita Brens said police were keen for Mark to officially come forward, report the incident and hand over any footage.

“We urge that person to hand the footage into police,” Ms Brens said.

“It would form part of any evidence we may need to present."

Victoria Police and Metro yesterday urged people not to take the law into their own hands. Senior Sergeant David Cochrane, of the transit police, urged people not to approach offenders but to ring police or Crime Stoppers on 1800 333 000.

"Be aware of the risks involved and think carefully before you do it," he said. "In this case, the person has let the offenders know he was filming and he was about to arrest them ... and it appears he has been assaulted as a result of it, which is concerning to us," Sen-Sgt Cochrane said.

"If you see this stuff and you film it, we advise that you ring police.

"Please let the police know in the first instance, because you put the prosecution at risk by putting it straight on to YouTube."

Metro spokesman Daniel Hoare urged anyone who witnessed vandalism on a train or at a station to call police immediately.

"If someone sees graffiti being carried out on a train, we urge them to press the red emergency button on the carriage, which will activate a call to police," he said.

Metro must clean up graffiti within 24 hours of it being reported, which can force trains out of service.

Graffiti offences attract a $276 on-the-spot fine and possessing graffiti equipment on a train carries a $704 fine. Criminal damage carries a penalty of up to 10 years' jail.

Public Transport Users Association president Tony Morton said his group also did not encourage people to take matters into their own hands.

He said the video showed how a situation could get out of hand and distress other passengers.

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