A message was sent to a friend of runaway teenager Megan Stammers saying she had arrived in France after she is believed to have run away with her maths teacher.
It marked the last contact since 15-year-old Megan and 30-year-old Jeremy Forrest caught a ferry to the Continent last week, sparking a cross-Channel search.
The message was sent to one of her good friends saying she was in France but did not come from her own phone, a senior police officer revealed.
The disclosure was made as the teenager's mother and stepfather, Danielle Wilson and Martin Stammers, made an emotional appeal at a news conference for her safe return.
Chief Inspector Jason Tingley, of Sussex Police, said: "I can't give a specific time or date but we know there was a message passed to one of her good friends to say she had arrived safely in France. I can't say that message was from her but we believe it was. That gives us some comfort that she has arrived safely and she is in France. That's our last contact."
Last Thursday Megan asked her mother whether she could stay overnight at a friend's house. Her mother said she agreed, gave her dinner money for school the following day - and Megan left.
But the following morning, her mother received a text message from her school, Bishop Bell C of E in Eastbourne, East Sussex where Forrest teaches, saying she had failed to attend class. Checks were made to see whether the friend she claimed to be sleeping over with was at school, and when it was confirmed that she was, alarm bells rang.
Her family revealed that Megan had been receiving extra-curricular maths lessons since before the summer. But they did not suspect any relationship between her and Forrest, a married amateur musician, who lives in Ringmer, near Lewes.
Interpol, the UK Border Agency, the British Embassy in France and the French authorities were all working to help trace Megan.
Police believe that Megan and Forrest either planned a short break and intended to return yesterday evening or that the plan to come home was devised as a "smokescreen" to enable them to spend longer together.