The Lamplughs started the personal safety charity 17 years ago following the disappearance of their estate agent daughter Suzy, who vanished after showing a client a property in Fulham, West London.
Diana Lamplugh announced she was to step down as chairwoman in August after a stroke, but has now developed Alzheimer's after undergoing major surgery for a brain haemorrhage. As a result she has suffered almost complete memory loss, prompting her husband to leave the charity in order to look after her full-time.
The charity planned to recruit its first chief executive at some point over the next two years, but has now brought the search forward.
"This will obviously be a time of change for the charity," said Ann Ellege, trusts manager at the trust. "So far the trust has revolved around the Lamplughs' personalities, but I think we've grown to the extent that we will be able to move on and continue their good work."
Diana Lamplugh is a well-respected and prolific campaigner for personal safety and has established a wide range of courses for school children and adults. She also helped establish other personal safety charities such as Get Connected and Victims Voice, and received an OBE in 1992 for her charitable work.