The pair have been recognised by peta2, the youth division of the animal rights organisation People for the Ethical Treatment of Animals (Peta).
Zendaya saw off competition from fellow veggies including Anne Hathaway and Alicia Silverstone to earn the title, while MCGuiness was picked over actor/rocker Jared Leto, funnyman Russell Brand and Tony Kanal of No Doubt.
Zendaya is so dedicated to her meat-free diet, she asked writers of her Disney show Shake It Up to make her character Rocky Blue a vegetarian.
She explains, "In the meatball episode which was really gross, I put in a part where I said I was vegetarian because I really am a vegetarian in real life. That's something I believe in very strongly. We decided to make Rocky a vegetarian as well."