A new text service for people who are feeling suicidal or facing a mental health crisis has been launched by the Duke and Duchess of Cambridge who are calling for 3,000 members of the public to train as online counsellors.

Speaking at Kensington Palace, Prince William said a low-key trial of Shout had already seen 60,000 people “who were feeling scared, frightened and alone” contact the service with the most common issue being suicidal thoughts. So far, 85% of the users are under 25.

During the trial, ambulances had to be called out for people who were using the text service and were considered at active risk of hurting themselves on average twice a day.

“As texting is private and silent, it opens up a whole new way to find help,” the Duke said. “You can have a conversation anywhere, at anytime: at school, at home, anywhere.”

Prince William, Duke of Cambridge, meets crisis volunteers working with Shout. Photograph: Handout/Shout via Getty Images

The Duchess of Cambridge said: “It’s able to offer support when it is crucially needed and the opportunity to turn lives around. This really is an important step for those desperately in need.”

The service is separate from the Samaritans which already operates a phone line and an email service using 20,000 volunteers who answer more than 5 million calls a year, the equivalent of one every six seconds.

Shout will allow people to open up a text chat with a volunteer working remotely, most likely at home, who has been trained to listen, reassure and guide people.

All the text conversations are anonymous, unless the client wants to give their name, and are reviewed in real time by a panel of qualified psychotherapists who can take control if they feel there is a problem in the direction of the discussion.

Artificial intelligence determines the priority for handling each case based on what is written in each initial text. When words like suicide, forced marriage and slavery crop up, the case is prioritised.

“[Volunteering] is not for everyone,” said Prince William, who has previously told how his first assignment when he worked for East Anglian air ambulance was to a male suicide. “There are some very difficult conversations. You need to be able to listen without judgment on a range of issues from suicidal thoughts to bullying, abuse, sexuality, self-harm and relationships.”

Each volunteer will be asked to commit to the training and 200 hours of volunteering a year. One of the current volunteers, Jo Owen, said the service worked for those who find face-to-face discussions about difficult issues daunting and was for “people like me who can only find the words with their thumbs”.

A similar system in the US has been operating for five years and has handled 100 million texts, with spikes around moments such as the suicide of the comedian Robin Williams and the broadcast of the Netflix series, 13 Reasons Why, about a young woman who takes her own life.

In the UK in 2017 there were 5,821 suicides with the highest rate for men aged 45-49.

The UK male suicide rate is the lowest in more than 30 years. It decreased by 3.1% between 2016 and 2017 and has been falling since 2013. The female suicide rate also decreased by 2% in the last year recorded by the Samaritans. However there were rises in suicide rates in Wales and Northern Ireland.

Shout will be funded with money from the Royal Foundation, the primary philanthropic and charitable vehicle for the Duke and Duchess of Cambridge and the Duke and Duchess of Sussex. Information about the service and volunteering can be found at giveusashout.org