Whaite, who won The Great British Bake Off in 2012, took to Twitter to ask for help.
"My sister has gone missing from Faro Airport," he wrote, "We are all worried for her welfare. Portuguese police aren’t interested in helping us search for her".
Whaite also revealed that his sister, Victoria Cunningham, does not have a passport with her.
He wrote that she had been unable to board a flight on Saturday, and that on Monday afternoon she was due to take a flight, but left Faro airport without money or her passport.
"Apparently she headed towards a petrol station in Faro.
"My other sister Jane and friend Chris are flying out now to try and find her.
"She is vulnerable and could pose a risk only to herself.
"If you see her please tell her that her family just want her home safe and sound," he tweeted.