A 30-year-old man believed to have run away to France with a 15-year-old schoolgirl is one of her teachers, sources say.
Police have appealed to Jeremy Forrest or Megan Stammers to make contact after eloping across the English Channel.
It is believed that Forrest is a maths teacher at the same school that Megan attends, Bishop Bell C of E School in Eastbourne, East Sussex.
There have been no reported sightings or contact with the pair since they vanished, and police were tonight pursuing "critical lines of inquiry".
The alarm was raised at mid-day on Friday after Megan failed to turn up for school. Nine hours later she crossed from Dover to Calais, sparking an appeal to trace her.
Police have said they do not believe Megan is at risk but they are in contact with the French authorities in an effort to reunite her with relatives.
Her father, Martin Stammers, said: "We just want Megan to make contact with us. We are worried and miss her terribly. Please get in touch, Megan."
Chief Inspector Jason Tingley said they were at a "critical stage of the investigation" and officers were grateful for the support of Megan's family and friends.
Appeals for information about her whereabouts have been posted on Facebook and Twitter, including from her worried father.
He tweeted: "Have to remain strong for Meg's, can't dwell in the misery of 'what ifs' - we love you sweetheart, doing all we can #findmeganstammers."