The motive for Mr Dewji’s abduction is still unclear
Financial magazine Forbes puts his wealth at $1.5bn (£980m), and has described him as Tanzania’s only billionaire.
In a 2017 report, it said Mr Dewji was Africa’s youngest billionaire.
He promised in 2016 to donate at least half his fortune to philanthropic causes, Forbes said.
Mr Dewji, locally known as Mo, is credited with turning his family business from a wholesale and retail enterprise into a pan-African conglomerate, reports the BBC’s Athuman Mtulya from Dar es Salaam.
His company, METL, has interests in textile manufacturing, flour milling, beverages and edible oils in at least six African states.
Environment Minister January Makamba, a friend of Mr Dewji, tweeted that he had spoken to Mr Dewji’s father and the family confirmed that he had been kidnapped.