|Police released CCTV footage of the three girls at Gatwick Airport|
Shamima Begum, 15, Kadiza Sultana, 16, and an unnamed 15-year-old, pupils at Bethnal Green Academy, flew from Gatwick on Tuesday, during half-term.
Commander Richard Walton, of the Metropolitan Police, said he feared they were "extremely vulnerable".
The trio are friends with a fourth girl who travelled to Syria in December.
At the time the three girls were interviewed as her friends, police said.
Cdr Walton said the teenagers' families were "devastated" but there was a "good chance" the girls were still in Turkey.
He hoped a police appeal, via social media, would persuade them not to enter Syria.
They were last seen at their homes on Tuesday morning when they gave their families "plausible reasons" to be out for the day, police said.
The girls boarded a Turkish Airlines flight, which landed in Turkey on Tuesday evening.
The third girl is not being named at the request of her family.
Shamima is possibly travelling under the name of her 17-year-old sister Aklima Begum, police said.
Cdr Walton said he hoped the trio would "hear our concerns for their safety and have the courage to return now, back to their families who are so worried about them."
He said the force was becoming "increasingly concerned" about a growing trend of young girls showing an interest or intent in joining Islamic State.
"The choice of returning home from Syria is often taken away from those under the control of Islamic State, leaving their families in the UK devastated and with very few options to secure their safe return," he said.
"If we are able to locate these girls whilst they are still in Turkey we have a good possibility of being able to bring them home to their families."
Shamima and the unnamed 15-year-old were reported missing by their families on Tuesday evening, while Kadiza was reported missing on Wednesday morning.
|Kadiza Sultana, aged 16, is the oldest |
of the trio, who are all in
the same school year
Kadiza Sultana is 5ft 6in and slim build. She was wearing black rimmed glasses, a long black jacket with a hood, a grey striped scarf, a grey jumper and dark red trousers and was carrying a black holdall. She speaks English with a London accent and Bengali.
Shamima Begum is 5ft 7in. She was wearing black, thick-rimmed glasses, a black hijab, a light brown and black leopardprint scarf, a dark red jumper, black trousers and a jacket, and was carrying a dark blue holdall with white straps. She speaks English with a London accent and Bengali.
The 15-year-old unnamed girl is 5ft 6in and slim build. She was wearing black, thick-rimmed glasses, a black headscarf, a long dark green jacket with a fur-lined hood, a light yellow long-sleeved top, black trousers and white trainers, and was carrying a black Nike holdall. She speaks English and Amhrick.
|Shamima Begum, 15, could be|
travelling under the name of
Salman Farsi, a spokesman for the East London Mosque, said: "They have been misled. I do not know what was promised to them. It is just sad.
"I think the girls need to know they have done nothing wrong. They have been manipulated."
"The reality is quite grim and the terrain very harsh especially for such young individuals", said Dr Erin Saltman, from the Institute for Strategic Dialogue, which offers independent expertise in counter-terrorism, said IS propaganda targets young women specifically with the promise of being part of a humanitarian movement.
She said: "They are the wives and mothers of the future jihadists so quite a lot of dedication and time has been put into trying to allure these younger women to come and join in these efforts.
|Dr Erin Saltman, Institute for Strategic Dialogue|
"To be able to leave the house they need permission. They are only to leave if they want to pray or if there is a dire medical situation."
A fellow pupil at Bethnal Green Academy, identified only as Sadek, urged the trio to return. He said: "It's really sad what's happened and I think the government should try its best to help in any way, find out what happened and try to help the family as well.
"They need to educate people more, tell them about the risk of going to Syria, that it's not safe out there."
It's more than not safe, it's insane. I love the idealism of young girls, but when it draws them into situations like this it is both unfortunate and dangerous.
|CCTV captured the girls passing through security at Gatwick Airport|