Police searching for missing teenager Jayden Parkinson have told ITV News that a number of factors surrounding her disappearance prompted them to launch a murder investigation.
Commander Superintendent Christian Bunt from Thames Valley Police said the fact that the teenager had "no access to finance" and had not used a telephone since she went missing on Tuesday had changed the nature of the investigation.
"She didn't have any additional clothes and she hasn't been on social media, which is highly unusual for a 17-year-old," he said.
The investigation into the disappearance teenager Jayden Parkinson is focusing on the village of Upton and a grassed area off Lydalls Road in Didcott, Commander Supt Christian Bunt told Sky News.
He said: "We have got two significant search areas at the moment. We continue to focus on the area in Upton just outside of Didcot and we understand that is having a big impact on the local community.
"We've got a lot of resources attached to the operation, over 100 officers, specialist search and investigative officers and it's also important to mention we have specialist officers with the family supporting them".
Police investigating the disappearance of Jayden Parkinson have said they are planning to scour a rural area in Upton for "up to a week".
Detectives said they are looking for a man spotted in Upton carrying a large suitcase. Detective Chief Inspector Andy Murray told a news conference that the man was notably struggling to "manage" the heavy case.
Jayden's family are distraught, police said, as they announced their missing persons investigation into her disappearance had been changed to a murder inquiry.
Detective Chief Superintendent Andy Murray said the family still have hope.
"They've still got hope but they are distraught and they want their daughter to come home.
"I'm afraid the detective in me leads me to conclude that Jayden may well have been murdered and that's why we have approximately 50 detectives out there still trying to find Jayden, still trying to find evidence that might lead to somebody being convicted if she has been murdered."
Detective Chief Superintendent Andy Murray said police were now focusing on trying to find a man who was seen with a large suitcase in a field in the small village of Upton in the early hours of December 9.
That suitcase was large, it was heavy, it was difficult to manage and that man was having difficulty removing that suitcase from that area.
The man has been described as about 20, white, about 5'6" tall of medium to slim build, with short dark hair. The suitcase was described as light coloured, probably made of canvas material.
Police searching for missing teenager Jayden Parkinson in Oxfordshire have confirmed their missing person investigation is now a murder inquiry, despite no body having yet been found, and they are searching for a man seen with a suitcase.