The Office star, Mackenzie Crook, has asked the public to help him look for his missing sister-in-law.
Crook, 51, reported that Laurel Aldridge, 62, has not been seen by friends or family since Tuesday (14 February).
The actor has described the situation as 'incredibly difficult'.
Crook has since revealed to fans that his sister-in-law has been missing for nearly a week now.
Following Aldridge's disappearance, The Pirates of Caribbean star has reached out to the public for their assistance in locating her.
Speaking on BBC Radio Sussex, Crook explained: "It's incredibly difficult. She is in quite a vulnerable position at the moment."
"She missed a chemotherapy session on Tuesday, so we're really worried about her," he added.
While Crook noted that there have been 'reported possible sightings' of his sister-in-law 'as far north as Bignor Hill', these reports have since been 'discounted'.
"We think she is very much in the local Walberton area," Crook said.
The actor also told ITV News that Aldridge's disappearance was totally 'out of character'.
"She left her house early Tuesday morning and she's not been seen since," he continued.
"That's in the Walberton area where a lot of people are looking in the local woodlands along the roads and stuff like that."
Due to the busyness of the area, Crook reached out to people who live locally that could assist with the search.
He said: "I'd really like to appeal to people to go out into their back gardens and have a look in places where she might have taken rest."
"She's been missing out for three nights - we're entering the fourth one now [so], we're obviously really worried," he added.
Crook also asked the public to 'check again' for any further information of Aldridge's whereabouts.
"If I could appeal to everyone," he added, "even if they checked before, check again in likely places where she might have crept in to lay down for the night."
Crook said that his sister-in-law was last seen wearing a blue fleece with a grey coat, a brown woolly hat and black trousers.
They posted: "We’re growing increasingly concerned for Laurel Aldridge, who has been missing from Walberton, near Arundel, since yesterday."
It continued: "She may have travelled as far north as Bignor Hill, and we’re urging anyone who sees her to please call 999 quoting 347 of 14/02."Featured Image Credit: Shutterstock/Sussex Police