Reading Whisper is like "watching a trainwreck," one user told Business Insider. It's hard to pull your eyes away. The two-year-old app is rapidly gaining popularity. Millions of people use ...

In April, a 16-month-old Whisper competitor, Secret, went out of business. A memo written by Secret's CEO, David Byttow, stated that the app had 15 million users at its peak. There's a big ...