Detectives looking for a teenager who went missing 10 days ago have released a CCTV image of the last known sighting of her.
Jayden Parkinson, from Oxford, was last seen leaving Didcot Parkway train station at 4.27pm on December 3 - and did not return home that evening as planned.
A 22-year-old man and a 17-year-old boy have been arrested on suspicion of murder and remain in police custody.
Police said the 22-year-old, who is from Reading, Berkshire, is in a relationship with Jayden.
Detective Chief Superintendent Andy Murray, of Thames Valley Police, told a news conference the man was "part of our enquiries to prove or disprove whether Jayden has come to harm".
He revealed information had come to light to focus the search for the teenager in certain areas, including a wide, rural area between the village of Upton and Didcot.
Appeal: Superintendent Christian Bunt (L) and Det Ch Supt Andy Murray (R)Mr Murray said teams had been deployed to search a path or track leading from Upton in the general direction of Didcot, partly following a disused railway line.
He said: "We do not know where Jayden is at the moment, but as time progresses it is obvious that we are becoming increasingly concerned about her welfare."
He added officers remained "focused on the hope that she is still out there".
Jayden is described as slim, with shoulder-length dark brown hair and brown eyes.
She was living with her mother in Didcot until November this year, when she found herself homeless.
The teenager relocated to an Oxford service called One Foot Forward, which offers assisted and supported accommodation for young people.
Inspector Chris Simpson, leading the search, said: "She has little access to money and she has not been in phone contact which is out of character for her.
"She could be in Oxford or Reading areas with friends and if this is the case we would urge her or them to get in contact.
"Jayden is not in any trouble but we need to get in touch with her to ensure she is safe and well."
Anyone with information has been urged to contact Thames Valley Police on 101 and quote URN 542 10/12, or Crimestoppers anonymously on 0800 555 111.
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