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.”.
Police officers, mountain rescue teams, sniffer dogs and HM Coastguard air support are involved in the search, which has covered 100 miles.
Police are “increasingly concerned” as a major search continues for a young runner who has been missing for four days.
On Friday, the search concentrated on running trails Ms Hall often uses between Eggleston and Hamsterley.
Digital intelligence officers have checked Ms Hall’s mobile phone, smartwatch and running apps, but have found no leads.
