Counter-terrorism officers are hunting for the 15-year-old from Bristol and another girl, a 17-year-old from Lambeth, south London, who flew to Turkey last week in the hope of crossing into Syria.
Last night, as her mother Safiya Hussien wept and begged for her safe return, it was claimed the officers fear Yusra could have made contact with a dating site called Jihad Matchmaker.
'We are a Muslim family, we do things that need to be done but we are not here to talk about ISIS, we are here to talk about Yusra.'
Yusra, who is thought to have been exposed to jihadi propaganda on the internet, boarded a flight to Istanbul under the noses of police and border control officials at Heathrow.
She is believed to be with a 17-year-old girl from Lambeth, South London, whom she arranged to meet at the airport, and to have flown to Turkey in order to enter Syria, where Islamic State fighters control large areas.
Haras Rafiq, an outreach officer for the counter-extremism think tank the Quilliam Foundation, warned Yusra may have gone to become a jihadi bride.
He said: 'We suspect what's happened is that she met up with somebody here in London, she travelled from Bristol to London, so she already had this romantic notion.
'She already probably believes that she's going to go and get married so one of two things will happen.
'It's more than likely that she will actually go and become a jihadi bride. She at the age of 15 will marry somebody who she considers to be a holy warrior.
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