The free app from Samaritans scans for tweets involving phrases such as "tired of being alone", "hate myself", "depressed", "help me" and "need someone to talk to".
If the message poster's Twitter followers have the application, they will receive an email which links to the tweet that has been picked up, and offers guidance on how to provide support.
Designed by digital agency Jam, the Samaritans Radar app is aimed at Twitter users aged 18-35, who are the most active on social media.
"We know that people struggling to cope often go online looking for support," said Joe Ferns, Samaritans' executive director of policy, research and development.
"However, there is still so much we need to learn about why this happens and how we can make the online environment safer for vulnerable people.
"By not addressing this issue we run the risk of shutting these discussions down and driving them underground.
"Instead we need to use tools such as Samaritans Radar to encourage people to look out for one another online, helping them to reach out and offer support."
Patricia Cartes, Twitter's global head of trust and safety outreach, hailed the Samaritans for "experimenting with new ways of supporting people in the digital space".
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