The man, 19, will instead serve his one year and 10 months' imprisonment in the community under the strict conditions of an intensive corrections order for blackmailing the man, who said in court the attack was "a form of bigotry".

An ACT Supreme Court judge also ordered the offender, whose name has been suppressed, complete 250 hours' community service in the next 12 months.

He was among five males police charged after they cracked an extortion ring that targeted gay men on social media and threatened to "out" them as paedophiles unless they handed over cash and mobile phones in a string of attacks across the ACT.

One of the victims - described by his mother as "a beautiful drag queen" - killed himself hours after he was threatened by members of the group earlier this year.

Four of the teenagers who pleaded guilty over their crimes have been sentenced in the Childrens Court, including the adult offender's younger brother.

The man pleaded not guilty in the ACT Magistrates Court to blackmail, but later switched his plea to guilty.

Court documents said the man's younger brother, then 16, set up a fake profile on the over-18s gay hook-up app and agreed to meet with the victim at Mawson playing fields on January 7.

The brothers both showed up and the offender got out of his car and greeted the victim with the words: "Hi, I'm the paedophile hunter."

"So you have come here to see my little brother, he is only 15," he said.

The victim tried to leave as the offender said they could "sort this out" and the man didn't have to ruin his life.

The man questioned what they wanted and the brothers said: "We are kids, what do you think?

He asked: "Money?" The siblings had nodded before the man drove off.

The offender wrote of the extortion in a text message to a friend the next day saying he'd never "hunted pedos before and it's f---ing scary".

He faced a sentence hearing in August, when prosecutor Sara Gul said the "premeditated, planned, calculated" ambush was driven by greed and masked as "some kind of justice crusade".

The teenager's defence barrister James Stewart said he had been barely a man when he committed the offence and was "foolishly tagging along with his younger brother".

Chief Justice Helen Murrell took into account the man's 23 days spent in jail had been "a hard lesson" but had described the "vigilante" offences as "abhorrent".

She sentenced him to one year and 10 months imprisonment, but stopped short of deciding how that time should be served.

The case had been adjourned so the man could be assessed as suitable for an intensive corrections order.

The man's brother, 17, was sentenced to 19 months' youth detention, to be suspended from mid-August upon him entering a 12-month good behaviour order, for his role in the extortion.