“We are extremely concerned for the safety of these young girls and would urge anyone with information to come forward and speak to police,” Commander Richard Walton of Scotland Yard's counterterrorism unit was quoted as saying by the Telegraph.
The three girls met up at Gatwick airport and traveled to Istanbul on February 17 after giving their families “plausible reasons” for why they would be out for the day.
Police now fear that the girls, described as straight-A students at the same east London school, may be seeking to cross the border into Syria.
"It is an extremely dangerous place and we have seen reports of what life is like for them and how restricted their lives become,” Walton said, noting that the girls may not be allowed to travel back home if they join ISIL.
British law enforcement is reaching out to the missing girls through Turkish media and social media, hoping they return home to their worried families, Walton said.
Several British schoolgirls have recently made headlines after traveling to Syria to join Islamist militant groups.
Last year, 16-year-old twin girls ran away from their home in Manchester and boarded a plane to Turkey, later crossing the border over to Syria.
Another aspiring ISIL member, aged 15, was stopped from traveling to Turkey in December last year, when the plane she had boarded was stopped by police on the runway.
