British support group launched a service on Facebook on Monday to help people who express suicidal thoughts online.
Facebook users who see a friend has posted status updates or wall posts that suggest they may be considering taking their own life will be able to report them confidentially to Samaritans via the website's help centre.
The charity, which provides confidential emotional support, will then contact the person via email asking if they need help and counselling.
The initiative was unveiled just weeks after it emerged that a British charity worker left a suicide note on Facebook but none of her 1,082 friends on the site responded. Some even mocked her note.
"Took all my pills be dead soon so bye bye every one," wrote Simone Beck, 42. She died within 24 hours, causing her distraught family to ask why none of her online contacts had helped her.
"As a friend you are better placed to know whether someone close to you is struggling to cope or even feeling suicidal," said Samaritans chief executive Catherine Johnstone.
She added: "Facebook is a part of daily life for so many of us and we must make sure that people online have support when they need it."
Samaritans has already teamed up with Google so that when someone in Britain searches online for information about suicide, a red telephone icon with the charity's phone number is automatically triggered.