While there are no official figures on the number of Americans abducted overseas, Ms. Briggs said it’s roughly 200 a year. “This is still an unknown crime,” she said.

Her organization does not conduct hostage negotiations, Ms. Briggs said, seeing that as the purview of law enforcement and security officials. But it can prepare a hostage’s family for what to expect and the questions that should be asked.

Ms. Briggs played an indirect role in easing a strict United States government ban on contact with kidnappers, a change made a few years ago by President Barack Obama after the Islamic State had beheaded American captives.

Acknowledging that his administration had failed the families of those captives, Mr. Obama said that going forward, the United States government could under some circumstances negotiate with hostage takers. While he did not relax a ban on paying ransoms, he also said communication would be permissible between hostage takers and “the families of hostages or third parties who help these families.”

Mr. Obama also said families should not be threatened with criminal charges if they sought to pay ransoms, as happened to the parents of James W. Foley, an American journalist who was the first of the American captives held by the Islamic State to be beheaded.

Diane Foley, Mr. Foley’s mother and a critic of how the Obama administration had handled his case, said her advocacy for hostage families had been partly inspired by the work of Ms. Briggs. They became acquainted when the Foleys sought help from Hostage UK, and grew closer after Mr. Foley had been killed.