These 15-year-old twins are the reigning queens of Musical.ly, the Generation Z app that was just bought for ~$1 billion

Matthias Nareyek/Getty Lisa and Lena Mantler, 15-year-old twins from Germany, have one of the fastest-growing fan bases on the internet. You've probably never heard of them, but the teen in your life has. The girls are the reigning queens of Musical.ly, the social-media app of choice for Generation Z. Teens record and post 15-second clips of themselves lip-syncing, dancing to popular music, and pulling stunts. The app launched in 2014 and has racked up over 200 million "musers." In November, the...