Gillian was last seen at her home in Patcham on August 23, 2017.
She had gone out for a walk but did not return home, before being reported as missing on August 24.
Police have been searching tirelessly for Gillian since that day and, just over five years on, are once again appealing for any information which could help locate her.
At the time of her disappearance Gillian was described as being 50 years old, white, 5’6″, of medium build and with shoulder-length brown hair.
She would now be 54 years old.
She was last seen wearing a thin blue or grey 3/4 length sleeve top, a grey ‘stone’ effect Peter Storm waterproof jacket, brown ankle boots, a knitted grey scarf and carrying a small grey Karriemor rucksack.
PC AJ Funnell, of Brighton and Hove’s Missing Persons Team, said: “When Gillian was reported missing five years ago an investigation was immediately launched into her disappearance, and our commitment to finding her has not dimmed.
“Anybody who has any information which could help with the investigation, no matter how small you may feel it is, please report it to us online or by calling 101.”