When your phone is low on storage, what's the first thing you delete? Photos of your ex? Old podcasts you'll never listen to? Cat memes? One app you might not have considered turning to is Facebook.

Facebook’s free dating service has 21 million users, more than the popular dating app Hinge, as the social network reinvents itself. By Eli Tan Reporting from San Francisco For years, Alyssa Landguth, ...