The case of three Colorado teenagers who flew to Germany to join the Islamic State group is a model example of terrorist recruitment by social media, a report cited in the Denver Post said Tuesday. The suburban Denver girls were just a few among hundreds enticed to join the terror organization in Syria by such methods.

The Colorado girls, a 16-year-old girl of Sudanese descent, and two 15- and 17-year-old sisters of Somali descent, shared militant recruitment videos, the Search for International Terrorist Entities Intelligence Group, also known as SITE, said Tuesday. One of the videos they posted included Anwar al-Awlaki, an American who became an Qaeda-leader. He was later killed a Yemen drone strike by the U.S. in 2011.

"The girls followed online jihadists from around the world, including the United Kingdom, Canada, the Netherlands and Syria," Rita Katz, director and co-founder of the Bethesda, Maryland-based nongovernmental organization, said in her report.  “Online recruiters have successfully won over Westerners, including Americans.”

The girls purchased their tickets in cash, but they never made it to their final destination. German authorities, who acted on a tip from the FBI, stopped the girls in Frankfurt before they made their way to Syria, the Denver Post said.

The teens were brought back to the U.S. two days later. Their identities have not been revealed because they are juveniles and out of privacy and safety concerns, the Denver Post said. They have not been charged.

How were the teens radicalized? Multiple signs seem to point to social media.

"The process they underwent-- from use of social media, radicalization, recruitment online, even through the actual travel route to join the Islamic State -- all follow the exact same pattern shared by several hundred Westerners," wrote Katz, who has called the girls' attempted trip a "case study."

In addition to following online jihadists from around the world, the teens followed the Twitter account "Jihadi News," which is the same account followed by Martin Rouleau. Rouleau, 25, drove his car into two Canadian soldiers in Quebec last month, killing one, and then committed suicide. They also followed the account "Women of Islam," which encourages women to make sacrifices for the sake of jihad, and they followed an account under the name "Sara," where YouTube jihadi lectures would be constantly tweeted.

In fact, all three of them spent extensive time on social media sites like Instagram, Twitter and Facebook, SITE said. Each of the girls has thousands of tweets, with the highest amount being 13,000.

"What it really demonstrates is the tremendous power of social media," Jonathan Adelman, a professor at the University of Denver's Josef Korbel School of International Studies said, according to the Denver Post. "They are out there on Facebook. They are out there on Twitter. They are reaching out without any intermediaries."

Recruitment is reportedly a priority for ISIS for both males and females, but there has been an emphasis on luring women after the group announced the goal of building its own nation, SITE wrote. In a recent campaign, Muslim females of all ages are encouraged to leave their homes for Syria. That campaign reached the Colorado teens.

“The campaign provides the propaganda, the communications, and the information on why--and very specifically how--Muslim females of all ages must leave their homes and travel to Syria,” Katz said.

There are reportedly 100 Americans who have joined the Islamic State. The FBI reportedly knows who these people are and are monitoring them in case they decide to return to the U.S.

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