Ms Tunzi emerged top in the contest after impressing the judges and fans through the different rounds with different outfits.
Miss Puerto Rico, Madison Anderson and Miss Mexico, Sofía Aragón emerged as runner-ups.
During question time Ms Tunzi said that the most important thing that girls needed to learn was leadership.
"It's something that has been lacking in young girls and women for a very long time not because we don’t want to but because of what society has labelled women to be. I think we are the most powerful beings in the world," she said.
Ms Tunzi had been running a campaign online where she urged South African men to write what she described as love letters to the country's women.
She went on to incorporate the letters in her national costume outfit that also featured the South African flag colours.