The app, called Samaritans Radar, looks for specific keywords and phrases within a tweet then sends an email alert to the user with a link to the tweet and offers guidance on how to provide support.
The app has been developed on the back of research that suggested people who had committed suicide were more likely to have published a greater number of tweets than usual beforehand. In addition, with the help of academic experts, phrases have been identified that vulnerable people use on social media.
Joe Ferns, executive director of policy, research and development at Samaritans, said: "We know that people struggling to cope often go online looking for support, but 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. 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, added: "Twitter actively forges partnerships with organisations in the field of online safety and digital citizenship, and Samaritans has a longstanding reputation for supporting people in times of need. It is fantastic to see it extending this expertise and experimenting with new ways of supporting people in the digital space."