Three teenage girls have returned to Colorado after they reportedly tried to join ISIS forces in Syria.

The three, who are facing investigation, were victims of an “online predator” who encouraged them, a school official said Wednesday, as U.S. officials tried to determine how they made it to Europe without anyone knowing and whether terrorists’ appeal is deepening among vulnerable youth.

The Denver-area girls — two sisters ages 17 and 15, and their 16-year-old friend — were detained at the airport in Frankfurt, Germany, and sent home over the weekend. They were interviewed by the FBI and returned to their parents in suburban Aurora. Those in the tight-knit east African community where they live said the sisters are of Somali descent and their friend is of Sudanese descent.

The episode posed vexing questions for U.S. officials, including about the use of social media by terror groups to recruit people inside the United States and what can be done about it.

“Social media has played a very significant role in the recruitment of young people,” said FBI spokesman Kyle Loven in Minneapolis, home to the largest Somali community in the U.S. Authorities there have been concerned about terror recruiting of the young for years.

“What it indicates is we have to be really careful about people in impressionable years and what they’re doing on the Internet,” said Jim Davis, former special agent in charge of the FBI in Denver.

At least one of the girls was communicating with someone online who encouraged the three to travel to Syria, said Tustin Amole, a spokeswoman for the Cherry Creek School District where the girls attend high school.

Fellow high school students told school officials on Monday that the girls had been discussing travel plans over Twitter, Amole said.

“There’s no indication they had been radicalized in a way that they wanted …read more