When Nicola Benyahia's teenage son slipped away one day to join Daesh terror group in Syria, the frantic mother anguished over his disappearance for months while keeping it secret from her friends and most of her family.

"I kept it secret because of the shame of it," she told the Thomson Reuters Foundation. "We didn't know how to answer people because we couldn't even make sense of it ourselves. One minute we were just doing our daily life and the next day he was gone."

Hoping to spare other families such loneliness and despair, Benyahia this week launched Families for Life, a counselling service to help cope with the complexities of radicalization.

Thousands of fighters from the West have joined Daesh, and other radical militants in Syria and Iraq, according to the New York-based Soufan Group, which provides strategic security to governments and multinational organisations.

Some 850 of those fighters and supporters travelled from Britain, according to authorities, and about 700 from France.

They include teenagers like Rasheed Benyahia who became radicalised and, aged 19, made the drastic and, in his case, irreversible decision to leave home and fight.

Families for Life will help those worried about their vulnerable children and those grappling with children they have lost to violent radicalisation, said Benyahia, 46, who lives in Birmingham, Britain's second-largest city.

Her son, who was working at an engineering apprenticeship, left home on May 29, 2015, a day etched in her memory.

"That particular morning I missed him," she said. "He used to come down and give me a quick kiss and go out the door, but that morning I was a little bit late getting up and missed him."

The Benyahia family did not know where he was, or if he was dead or alive, until weeks later when he sent a message from Raqqa, a city in northern Syria, where Daesh runs training camps and directs operations.

The family corresponded with him sporadically by text and telephone in the months that followed.

WARNING SIGNS

That ended with a telephone call saying Rasheed Benyahia had been killed in a drone strike on Nov. 10 last year on the border of Syria and Iraq.

Before her son left, Benyahia said she saw no signs that could have predicted his fatal move.

With Families for Life, Benyahia, a trained mental health counsellor and therapist, also plans to work in prevention, such as speaking to school students.

But its most critical task may be helping families wrestling with feelings of shame, guilt and responsibility, she said.

Rasheed Benyahia had been convinced by someone - she still does not know who - that he was not a good Muslim if he did not join the Daesh terror group, she said.

"He was vulnerable, and somebody swooped in," she said.

While he was missing, she sought help from the Berlin-based German Institute on Radicalization and De-radicalization Studies (GIRDS) and Mothers for Life, a global network of women who have experienced violent terrorism in their families.

There was no such support in Birmingham, she said.

The city in central England, however, was the site of a bitter controversy two years ago about foreign fighters imposing extreme cultural norms and values in some schools.

"When I speak to people and they realize I lost my son through this, they start opening up and start disclosing their concerns," said Benyahia, who will join a panel next week on radicalisation at Trust Women, an annual women's rights and trafficking conference run by the Thomson Reuters Foundation.