British police are using social media and cell phone numbers to try to contact three London schoolgirls whom they fear left home with plans to travel to the part of Syria controlled by the ISIS terror group.  

Shamima Begum, 15, Kadiza Sultana, 16, and a third 15-year-old girl whose family did not want to identify her are close friends at Bethnal Green Academy in east London. They were last seen Tuesday morning after they left home, saying they were going out for the day.

But surveillance video revealed the girls traveled to London’s Gatwick airport and boarded a Turkish Airlines flight which landed in Istanbul Tuesday evening.

Police say the girls are close friends with another 15-year-old girl who fled to Syria in December.

"We are concerned about the numbers of girls and young women who have or are intending to travel to the part of Syria that is controlled by the terrorist group calling themselves Islamic State," Metropolitan Police Commander Richard Walton told Sky News.

"It is an extremely dangerous place and we have seen reports of what life is like for them and how restricted their lives become. It is not uncommon for girls or women to be prevented from being allowed out of their houses or if allowed out, only when accompanied by a guardian,” Walton told reporters.

The families of the girls are “devastated” but holding out hope that they are still in Turkey and can be stopped before heading to Syria. The teens brought cell phones with them so police are using Turkish media and social media to try to contact them.

"It's really sad what has happened,” a family friend of one of the missing girls, identified only as Sadek, told Sky.

Security checks for people departing from U.K. airports make it a "walk in the park for jihadis and girls like this" to leave, Former Metropolitan Police border control officer Chris Hobbs says.

"At the moment you go through security, you get on the plane, you might be checked by a private security guard," he said. “If you're on a watch list then you will ping the system. If you're not on the radar then the odds are you will get on the plane without too many problems."

The girls-- who are British nationals of Bangladeshi descent-- were all wearing Western clothes at the airport. Shamima was wearing black glasses and a hijab, Kadiza was also wearing glasses and a grey striped scarf, and the unidentified girl was wearing glasses and a black head scarf.  

"The choice of returning home from Syria is often taken away from those under the control of Islamic State, leaving their families in the U.K. devastated and with very few options to secure their safe return," Walton said.

The number of Westerners who have travelled to Iraq and Syria to join ISIS is thought to be about 3,000, including as many as 550 women, according to the London-based Institute for Strategic Dialogue.