Twenty-year-old João Valente Figueira reportedly left home on 7 February to go for a bike ride, and never returned.
The man is understood to suffer from epilepsy and, according to national newspaper Correio da Manhã (CM), had problems with drugs.
His mother, Anabela Valente, has made a desperate plea for help in getting João home.
He is understood to have left home on his bike on Tuesday, 7 February, at around 1.30pm, telling his mother he would return a few hours later, but failed to do so.
“The hours went by and I thought he may have gone to his father’s house, in Ferreiras, but the next day I found out he hadn’t,” she told CM.
João Valente had recently returned from Holland where he had been living with his brother for six months while undergoing treatment for drug problems.
“He accepted treatment and it worked, but he realised he needed psychological help. Now I don’t know why he ran away from home,” the man’s 54-year-old mother said.
He is understood to have run away from home before, several months ago, when he was found in Alcobaça.
João’s brother Nelson said in a Facebook post over the weekend that the young man had been spotted in a restaurant in Olhos de Água.
He was last seen wearing a red coat with white sleeves, a black cap, carrying a blue backpack on a red and turquoise bicycle.
Anyone with details about João’s whereabouts should contact the Albufeira GNR police on: 289 590 790.