A teenage predator who targeted young girls and left three lives in ruins has been jailed for nearly four years.

Regan Philip Burrell, 18, also blackmailed one of his victims - two of whom were 12 and one 13 - threatening to disclose explicit photos she had sent him via Snapchat if she did not meet him for sex.

When she did meet the Waitati man, in a car park in central Dunedin in May last year, Burrell locked her in the back of his car.

After a brief liaison, the girl pushed him away.

Burrell threatened to kill the victim's dogs and damage her father's car if she told anyone what had happened.

But in July, police discovered his depraved and ongoing acts and the teenager eventually pleaded guilty to blackmail, two counts of exposing a young person to indecent material, two of indecent assault and three of sexual connection with a young person.

He appeared in the Dunedin District Court last week where his victims finally had the chance to confront him.

Two tearful parents gave accounts of the profound impact the experiences had had on their daughters.

One victim had resorted to self-harm, the court heard, while another had been stripped of her dignity.

''You were reckless in the extreme, with no regard for my daughter who was at her most vulnerable,'' said one mother.

One victim faced her abuser and read her statement to the court. Since the trauma of last year, she said, she had all but given up on her schooling.

''I feel like my life has been completely destroyed,'' the girl said.

''I wish I could continue my life without this constant pain.''

Burrell's offending began in January last year, when he began sending regular messages asking a girl for sex.

Eventually she relented and the pair engaged in several consensual acts over a few months.

Judge Michael Crosbie stressed that was not the issue.

''It doesn't matter what you think about them consenting, they're too young to,'' he said.

Burrell met his second victim through the first and began grooming her with flirtatious messages. Within days they met in a secluded area of a Dunedin park, where the sexual contact took place.

The third girl only met up with Burrell because he repeatedly made threats about distributing her nude photos to her friends and family. He repeated the blackmail five times.

Crown prosecutor Catherine Ure highlighted elements of a psychologist's report which put Burrell at high risk of reoffending.

He had ''developed a range of distorted, anti-social attitudes that normalise sexual conduct with young females'', she said.

Burrell accepted what he had done but minimised the gravity of his behaviour, the court heard.

''You regularly maintained the behaviour was consensual and the victims were purposely and unfairly trying to get you into trouble,'' Judge Crosbie said.

''It tells me that you don't get it.''

There were also troubling aspects of the report he pointed to that suggested Burrell was a supporter of a gang and looked up to its members.

The judge hoped one-on-one counselling would start immediately while the teen was behind bars.

Counsel Anne Stevens QC said her client was showing signs of progress and was willing to work with clinical professionals.

She said the offending had stemmed from social isolation and ''a complete misunderstanding of relationships''.

Burrell's victim who spoke in court said she was determined to endure the pain she was suffering. And she took some solace in the truth being unveiled.

''Regan Burrell, you're a known sexual predator and now I hope you finally get to suffer,'' she said.

''People will know who you really are.''

Burrell was jailed for three years and 10 months.