Police say she was last seen at around 6pm on Wednesday (February 24).
Ms Nagel is described by police as a “white female, around 5ft 8in tall, medium build with long brown hair wearing a black wrap-around coat”.
Police believe she may have been driving a white Mazda 2 hatchback (registration FP67YJC).
Inspector Stephen Granger said: “We’re eager to establish Endellion’s whereabouts as soon as possible and are asking for the public’s help as part of this.
“Her family are very worried about her and we would urge anyone who believes they may have seen Endellion or her vehicle to contact us.”
Police are asking those with information to call Police Scotland on 101, quoting reference number 0456 of February 25.