Sussex Police via AFP - Getty Images

An undated handout picture released by Sussex Police on September 24, 2012 shows missing British teenager Megan Stammers. British police were liaising with French colleagues on September 24 in an effort to track down a missing 15-year-old girl said to have fled across the Channel with a married teacher twice her age.

LONDON -- A 15-year-old British girl is believed to have run away to France with her 30-year-old math teacher, ITV News reported.

Megan Stammers, of Eastbourne, England, was reported missing at about noon on Friday and police said they believed she had traveled from Dover, England, to Calais, France, that evening.

Police said later that she was believed to have left the country with Jeremy Forrest, 30, of Ringmer, near Lewes.

"Megan's family love her dearly and are all incredibly upset by her disappearance. They want her to come home as soon as possible. We need Megan or Jeremy to make contact with us to help us return her safely to her family," Chief Inspector Jason Tingley, of Sussex Police, said in a statement on its website Saturday.

Police said her family were due to appear at a press conference later Monday.

ITV News said a blog posted on May 19 on Forrest's website, James Ayre Music, talked about trying to deal with a “moral dilemma.”

“And the overiding question it left me with was this: How do we, and how should we, define what is right or wrong, acceptable or unacceptable???” the blog said, according to ITV News.

“I came to a few different conclusions, mainly that actually we get a lot of things wrong, but at the end of the day I was satisfied that if you can look yourself in the mirror and know that, under all the front, that you are a good person, that should have faith in your own judgement,” it added.

Read more stories from ITV News 

Megan’s sister Brooke said in a message on Twitter that “Hope and faith is all we can give and everyone's support is amazing.”

“Will not stop until my sister is home! #keepfaith #keephope #findmeganstammers,” she said in another message.

Her father Martin Stammers appealed for Megan to get in touch. “We are worried and miss her terribly,” he said.

A Facebook page has been set up called “Find Megan Stammers.” At 6:25 a.m. ET Monday, the page had 2,320 likes.

ITV News is NBC News' UK partner.

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