The mother of Kirsa Jensen who's presumed murdered after disappearing while out riding her horse 34 years ago says the Amber Alert system launched in New Zealand today could have changed the 14-year-old girl's story.

New Zealand Police have teamed up with Facebook, the biggest social media player in the world, to provide the Amber Alert tool that'll help investigators find lost children.

Kirsa Jensen disappeared while out riding her horse on Napier's Awatoto Beach in September 1983. She has not been seen since and is presumed murdered.

It was a case which gripped the nation, as Kirsa's mother Robyn Jensen made emotional appeals for help to find her.

The pain is something Ms Jensen doesn't wish on any other parent.

"The sheer and absolute hell of not knowing, knowing that something has happened to your darling child and hoping against hope that she was still alive," she said today.

Today appeals for help in a missing child case are no longer limited to flyers or media headlines, with the Amber Alert system available for the first time in New Zealand.

"If a child goes missing in your area you'll see an alert about the child right in the middle of your mobile device or on our desktop. It'll contain a picture of the child, a brief description, the name, the age, the last location where the child was seen," Emily Vacher of Facebook explained. 

Ms Jensen said: "It's the most ghastly, ghastly experience. And the assurance of Amber Alerts now, that's why I say it's an absolutely amazing innovation."

"If this technology had been available in 1983 it could have been a different story for Kirsa."

Detective Superintendent Tim Anderson said the investigator or police officer attending will weigh up the factors and speak with others if they have to and where there's a serious or imminent threat to that child's safety or harm an Amber Alert could be issued.

Amber Alert was first launched in the 1990s in the US after the disappearance of Amber Hagerman. Facebook started offering the feature in the US in 2015.

Child abduction is rare in New Zealand, with just eight disappearances in 80 years, and police hope to harness the power of Facebook's 2.9 million local users to stop it from happening again. 

"This initiative is a success if it makes a difference to just one child or young person," said Richard Chambers, Police Assistant Commissioner.