Justin Bieber sings "Happy Birthday" for the American Cancer Society

The American Cancer Society has added to its More Birthdays campaign, with musicians performing their own special renditions of “Happy Birthday.” Joining Justin Bieber are Jack Johnson, Colbie Caillat, Maroon 5 and other artists.

“Hopefully, me singing Happy Birthday to people through this effort will make them smile,” says Bieber. And help boost donations, of course.