Authorities in Portugal are said to be helping in the hunt for 72 year old Mr John Joyce, who has not been seen since last Friday when he was last captured on CCTV in the Portuguese town.
The pensioner's niece Catherine Hathaway has launched a Facebook appeal which explains her uncle went out without any money, bank cards or his passport.
She said: "He has been missing four nights now and we are increasingly worried."
Mr Joyce, from Sheffield, South Yorkshire, was attending a six day pilgrimage to the site north of Lisbon with a small group he travelled with on a plane from London Gatwick.
The town is where the Sanctuary of Our Lady of Fatima is located, where six reported visions of Mary to child shepherds took place a century ago.
According to missing persons website the Lucie Blackman Trust, which supports British people overseas, Mr Joyce met the group for breakfast then went to a video screening in a small studio. The group then went their separate ways.
His family have said he was last seen at 11am on July 14th, wearing shorts and a t-shirt.
The British Embassy in Portugal is understood to be helping in the hunt for Mr Joyce as well.
Sheffield Wednesday fans in Portugal for the Owls' pre-season tour are also being urged to look out for Joyce.
Anyone with information can contact the Lucie Blackman Trust on 0800 098 8485, email any information to [email protected], or contact the local Fátima GNR police on (+351) 249 530 580.