By Ellen Wulfhorst

NEW YORK (Thomson Reuters Foundation) - When Nicola Benyahia's teenage son slipped away one day to join the Islamic State 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 counseling service to help cope with the complexities of radicalization.

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

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

They include teenagers like Rasheed Benyahia who became radicalized 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 radicalization, 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 the ultra-hardline Sunni Muslim Islamic State 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 was 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.

But now in hindsight, she said she sees the warning signs and hopes her insight and experience will help families in similarly precarious situations.

For example, her son had switched to go to a different mosque from the one his family attended, and he refused to cut his hair, she said.

He also asked her to shorten his trousers to above his ankle, which she now realizes is a style worn by some strict Muslims.

With Families for Life, Benyahia, a trained mental health counselor 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 jihadists, 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 jihadist radicalization 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 over allegations of a hardline Muslim conspiracy to impose 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 radicalization at Trust Women, an annual women's rights and trafficking conference run by the Thomson Reuters Foundation.

"I've decided to fill in a gap that seems to be there."

(Reporting by Ellen Wulfhorst, Editing by Belinda Goldsmith)