Counter-terrorism experts believe a British teenager suspected of trying to join Islamic State (IS) militants in Syria may have been seduced online through a matchmaking service.

Yusra Hussien, 15, went missing from her home in Bristol on September 24. She boarded a flight from London Heathrow to Turkey that day, along with an as yet unidentified 17-year-old girl. It is thought that they were attempting to enter Syria across the Turkish border to join ISIS militants.

Security sources have now revealed that Hussein contacted the 'Jihadi Matchmaker' Twitter feed, which offers to help "link up those seeking marriage in Syria in a halal manner".

The service has denied affiliation with IS, but uses similar imagery to the extremist group. It invites those looking for a spouse to send a direct message including their background, status and location, telling them to put their trust in Allah.

According to the Mirror, the Home Office has closed down 30,000 terrorist-affiliated websites in the past nine months.

Hussein's parents yesterday read out a statement during a police press conference in Bristol, in which they called their daughter a "typical teenager" and urged her to return home.

"There have been many assumptions and speculations claiming that Yusra is travelling to Syria, that she may be an extremist, or that she is planning to become a jihadist bride, all of which have not, as yet, been proved with any concrete evidence," the said.

"We would like to make a request to the media to not state anything which is both incorrect and not backed by evidence.

"Yusra we are missing you, if you are watching this please contact us, you are not in trouble and we are not angry with you. We just want you back home with us."

Hussein's friends have reported that before her disappearance she had become fixated with viewing extremist material online.

It is thought she became "self-radicalised".