Victoria Cunningham, sibling of the Wrightington cook, disappeared from Faro Airport in Portugal on Monday afternoon. She left the airport with no more than £120, her brother said.
She had been unable to board a flight on Saturday, and was due to fly home on Monday afternoon instead, but left Faro airport without money or her passport.
Following the widespread appeal for information on her whereabouts, which was shared by several high profile figures, John posted: "I am delighted to say that Victoria has been found. She is alive, she is sober but she is very very distressed (it seems she was found JUST in time).
"A stranger recognised her and took her into her house. Each and every one of you, who has tweeted, shared and commented, has saved a life today. And I cannot thank you enough - you are all angels."
John, who won the baking show in 2012, went on: "We are now going to focus on getting her home and back in good health in the privacy and protection of our family. My gratitude to each one of you is undying. You’ve helped save a sister, a daughter and a mother - thank you."
He added: "I also must thank the media who have been so gentle and helpful in this matter.
"If you wish to continue to help, please research in depth PMDD. Spread the word and hopefully more lives will be saved."