Police are "increasingly concerned" as a major search continues for a young runner who has been missing for four days.

       Jenny Hall, 23, was last seen leaving her home in Tow Law, County Durham, just after 3pm on Tuesday.

       Her car, a red Ford Focus, was found on Wednesday parked on the B6278, near remote moorland between Eggleston and Stanhope.

       Police officers, mountain rescue teams, sniffer dogs and HM Coastguard air support are involved in the search, which has covered 100 miles.

       Durham Police said it would be scouring Hamsterley Forest, a popular spot for walkers and hikers where Ms Hall was known to run as well as surrounding areas.

       Police say the search continues despite the "challenging weather conditions and terrain".

       Hamsterley Forest spans 4,942 acres and is about 16 miles from the town Ms Hall is from.

       Digital intelligence officers have checked Ms Hall's mobile phone, smartwatch and running apps, but have found no leads.

       The search has also involved motorbike officers, specialised sniffer dogs and air support drones, as per BBC News.

       Chief Inspector Dean Haythornthwaite, of Durham Constabulary, said: "We have become increasingly concerned for Jenny since she was reported missing on Tuesday and have been exploring all lines of inquiry."

       Ms Hall is described as being white, six feet tall with very long dark brown hair, which may have been tied in a ponytail.

       She was last seen wearing a blue John Deere hoodie, dark jogging bottoms, and may have been carrying a green jacket.

       Teesdale and Weardale Search and Mountain Rescue Team (TWSMRT), which is working alongside police, said its team have searched more than 60 miles of paths and tracks in the forest so far, BBC News reports.

       Peter Bell, a volunteer said the biggest challenge is the "area size itself and the terrain," which is "muddy and boggy".

       A TWSMRT spokesperson previously thanked members of the public who offered to help in the hunt for Ms Hall, but said people trying to assist could "hamper the systematic search", as per the outlet.

       Ch Insp Haythornthwaite also call on families who may be visiting the area recreationally on Saturday to give officers space to conduct the search.

       He thanked people who had already provided the force with information.

       Police are urging anyone with any information to ring 999.