She found it hard to sleep, often broke down in tears and was "overwhelmed by the horror of it all" after her son's death, weeks before police swooped on the social media extortion ring and arrested four people in February.

"My beautiful, kind, gentle and loving son was snatched away from life," the woman wrote in a victim impact statement read in court.

"I often think of his last moments. He must have been so distraught and in such fear."

He was happy and excited about a work promotion and upcoming holiday when they celebrated his birthday days earlier.

Now she couldn't bear to tell the man's elderly grandparents overseas he was dead - a "kind deception" she said would haunt her.

"My heart is heavy all of the time and I feel this will be with me for the rest of my life.

"The loss of a child in such circumstances is horrendous. I am in such pain and grief."

Her agony was recounted in a sentence hearing for the boy, aged 17, who pleaded guilty in the ACT Childrens' Court to two counts of blackmail. Police say two men were contacted through social media, threatened, and preyed on for cash and phones.

The Crown said the boy's crimes - "masked as some kind of justice crusade against paedophiles" - preyed on vulnerable victims, involved "a strong homophobic element" and were driven by an "astonishing" level of calculation, greed and enjoyment.

Prosecutors Sara Gul argued the man's suicide, while not directly caused by the boy's offending, was a consequence of it.

"There is a nexus between the death and the offences of the young person."

But the boy's Legal Aid defence lawyer, Hugh Jorgensen, argued there was no evidence to suggest his conduct had "a causal connection" with the man's death.

The court heard members of the group exchanged messages with the man for a couple of days before they met at Mawson shops the night of January 20.

The defendant, who compiled detailed dossiers on men targeted by the group, took a photograph of the victim before the offenders allegedly asked him to withdraw cash from an ATM and hand over his mobile phone.

He visited the man's home, allegedly with his older brother, and spoke to him a few hours later. Police say the victim was found dead that afternoon. His death was not being treated as suspicious.

Soon after, the boy had posted a message, threatening to "show up at your door", on the victim's Facebook page.

The court heard he claimed he got the idea for his crimes from television and his father, who suffered sexual abuse as a child.

Mr Jorgensen said the scam was "not an attack on gay people per se, but those people [he] believed preyed on people under 18".

He urged the boy be given the chance to rehabilitate and said online comments expressing his shock and devastation over the man's death showed remorse.

"I'm honestly doing this to make the world a better place, but the fact [the victim]'s taken his own life sucks," he wrote.

Ms Gul argued the boy was "sorry not sorry" and pointed to another message that read: "I contributed to a sick bastard killing himself".

She pushed for a sentence of full-time imprisonment and said the court needed to send a strong message to young people about the power, importance and influence of their actions on social media.

"This is a new breed of offending. It is millennial offending, if you will. Use of social media for extortion and blackmail wrecks lives.

"In the case of [the victim], this had the most terrible of consequences."

Chief Magistrate Lorraine Walker reserved her decision. The boy will be sentenced on Friday.

Three other males remain before the courts.

If you or someone you know needs help, contact beyondblue on 1300 22 4636, Lifeline on 13 11 44 or Kid's HelpLine on 1800 55 1800.