Facebook revealed in 2015 it would use the alert system across its social media platform. Strict criteria means only urgent cases where a child is at risk of death or serious injury and there is information, such as a registration plate number, that can help the public find the child, will be used in an amber alert. Former FBI special agent Emily Vacher, who works as Facebook's director of safety and trust, said the alert was only sent out to people in the search area. "We will say that's about 160 kilometres around where the child goes missing," she said. "You don't want to make it too broad because you don't want people say in Sydney seeing a missing person in Perth.

"It's not about the quantity of people that get this alert; it is about the quality. "And by quality I mean people who are actually in the search area and have the ability to help bring that child home." The alert will be the second position in a person's news feed and include a photograph, description and police contact details. Users don't need to have location services activated for Facebook to figure out you're in the search area. "We look at a number of signals: things that users give to Facebook when they sign up, they may say what city they are in," Ms Vacher said.

"It's done in an automated way, and if we think you are in the area we will send the alert. "If you use any of the location products it certainly will give a more specific region that you are in, you will be more likely to see an alert than if you don't." It will come down to state and territory police to contact Facebook with an urgent child abduction case for the AMBER alert to be activated. Ms Vacher used the example of baby Victoria in Canada, who was rescued after a member of the public noticed a police alert on Facebook and recognised the suspect's picture. Ms Vacher worked in the FBI for 11 years, including on the child abduction rapid deployment team.

"It was our job when one of these happened, we had to be on a plane in three hours to get to wherever the child was," she said. "I have always said I want to put that team out of business. I want the community to come together to find the child before the agents can get on the airplane." Facebook's AMBER Alerts will be launched in Melbourne with police commissioners from around Australia on Thursday. "Abducted and missing children can have a profound effect on loved ones and the community as well as the child, which is why NSW is taking part in the national rollout," NSW Police Commissioner Mick Fuller said. "Social media is an invaluable tool and with over 15 million Facebook users across Australia, it is a vital resource to reunite children with their families quickly."