Millions of Americans have used social media to understand and communicate about the killing of George Floyd. But for many of those tracking protests, the go-to online tool hasn’t been Twitter or Facebook but Citizen, an upstart smartphone app.

In the past week, about 620,000 first-time users in the U.S. downloaded Citizen on Apple Inc.’s App Store and Google Play, according to analytics firm Sensor Tower. The app, which uses police-scanner communication and on-the-ground reports, notifies users of what’s happening near them,…

Read More