Many of these "Lost Boys", some as young as 13, have simply been dumped on the side of the road in Arizona and Utah, by the leaders of the Fundamentalist Church of Jesus Christ of Latter-day Saints (FLDS), and told they will never see their families again or go to heaven.

Mr Jeffs is also being sued by lawyers for six of the Lost Boys for conspiracy to purge surplus males from the community, and by his nephew, Brent Jeffs, who accuses him of sexual abuse.

Warren Jeffs' whereabouts yesterday were uncertain, but Utah officials said they believed he may be hiding in an FLDS compound near Eldorado, Texas, and they have contacted the Texan authorities.

Some have voiced concern that an attempt to corner the sect leader could provoke a tragedy like the 1993 siege of the Branch Davidian sect in Waco, Texas.

Jim Hill, an investigator in Utah's attorney general's office, told The Guardian yesterday: "From everything I've been able to discern about Warren Jeffs, he is someone who is capable of some very different things. Whether that includes a mass suicide, I don't know. But I worry about it all the time."

FLDS officials and the sect's lawyer, Rodney Parker, did not return calls seeking comment, but have previously argued that the Lost Boys were exiled from their communities because they were teenage delinquents who refused to keep the sect's rules.

Mr Hill said although the boys may have been rebellious, their expulsion had more to do with the ruthless sexual arithmetic of a polygamous sect.

"Obviously if you're going to have three to one or four to one female to male marriages, you're going to run out of females. The way of taking care of it is selectively casting out those you don't want to be in the religion," the investigator said.

Dave Bills, who runs Smiles for Diversity, a foundation in Salt Lake City set up by an ex-FLDS member to look after the Lost Boys, said it was difficult to estimate their numbers because they had been scattered. But Mr Bills said the figures could be "as low as 400 and as high as 1,000".

"They live every day like it's their last day and they don't care about anything," Mr Bills said. "They're told they won't have three wives, and they're doomed. But they all want to go back to their mums."

One of the boys, Gideon Barlow, said he was expelled from a FLDS community in Colorado City, Arizona, for wearing short-sleeved shirts, listening to CDs and having a girlfriend. He said his mother rejected him on orders from the sect's leaders.

"I couldn't see how my mum would let them do what they did to me," he told the Los Angeles Times. After his expulsion, he attempted to give her a Mother's Day present but she told him to stay away. "I am dead to her now," he said.

Joanne Suder, a lawyer representing some of the Lost Boys in a case against the sect, said there had been "a conspiracy to excommunicate young boys to change the arithmetic so there are more young girls available for polygamy."

She said some of the boys were simply driven out of town and dumped on the side of the road, leaving them traumatised. "I think anyone who finds themselves ousted from the only environment they ever knew and left in the middle of nowhere, and then is not allowed to be with their family and loved ones, and is led to believe that they can no longer go to heaven, is going to be troubled," Ms Suder told The Guardian.

Polygamy is illegal in the US, but the authorities have been wary of confronting the FLDS for fear of provoking a siege or inviting political attacks for religious persecution.

State investigators have also found it hard to persuade FLDS members to give evidence against Mr Jeffs. However, authorities in Utah and Arizona have recently increased the pressure on the sect's leader, Last week, a Utah judge froze FLDS assets, and the attorney's office in Mohave County, Arizona, charged Mr Jeffs for arranging a marriage between a 28-year-old married and a 16-year-old girl. If convicted he could serve up to two years in prison.

Mr Jeffs inherited the leadership of the FLDS three years ago after the death of his father, Rulon. Since then, he has ruled its enclaves on the Arizona-Utah border, in Texas and Canada with fearsome discipline. At the age of 49 he has reportedly fathered at least 56 children by 40 wives.

There have been no confirmed sightings of Mr Jeffs for over a year, but a photograph of a man resembling the sect leader was taken in January at the FLDS 1,700-acre Texas ranch near Eldorado.

Randy Mankin, the editor of the local newspaper, the Eldorado Success, said: "People on the ranch don't have contact with the outside world. Two men only do whatever is necessary to do their business."

What is the FLDS?

The Fundamentalist Church of Jesus Christ of Latter-day Saints split off from the Mormon church in 1890, when the mainstream faith disavowed polygamy.

The sect has communes in Utah, Arizona, Texas and Canada. It is the biggest polygamous group in the US.

What does the FLDS believe?

Polygamy allows a higher birth rate, increasing the "righteous" population. No man can go to heaven if he has less than three wives. The sect believes black people are inferior, the offspring of Cain. It teaches that America was first colonised by a lost tribe of Israelites and was visited by Jesus after his resurrection.

Who runs the sect?

Warren Jeffs, 49, inherited the leadership in 2002 after his father, Rulon, died. He has pursued a hard line against sect members deemed to fall short of "perfection", and has purged hundreds from the ranks, mostly men and boys. He is estimated to have 40 wives and 56 children. His whereabouts are uncertain but he is widely thought to be holed up in the FLDS compound outside El Dorado, Texas.

Who are the "lost boys"?