From Wikipedia, the free encyclopedia. Hayley Kiyoko Alcroft (born April 3, 1991), known professionally as Hayley Kiyoko, is an American actress, singer and dancer. She is best known for playing Velma Dinkley in Scooby-Doo! The Mystery Begins and Scooby-Doo! Curse of the Lake Monster as well as Stella Yamada from the Disney Channel film Lemonade Mouth. Description above from the Wikipedia article Hayley Kiyoko, licensed under CC-BY-SA, full list of contributors on Wikipedia.