The application, which follows a long campaign by the Child Exploitation and Online Protection Centre (CEOP), appears on a user's profile page when they add or bookmark it and allows children and teenagers to report suspicious or inappropriate behaviour.
Particularly aimed at users aged 13 to 18, it also provides help, advice and support about staying safe online.
"We know from speaking to offenders that a visible deterrent could protect young people online," said Jim Gamble, chief executive of CEOP.
An automatic message will appear on the Facebook homepage of all teenage users, inviting them to add the application.
Pressure to introduce such measures intensified towards the end of last year after 17-year-old Ashleigh Hall was kidnapped, raped and murdered by a man posing as a teenager whom she had met through Facebook.
"Together we have developed a new way of helping young people stay safe online," Joanna Shields, Facebook's vice president for Europe, Middle-East and Africa, said of the link-up.