Snap Inc. reported its first quarterly decline in daily users, sending its stock price gyrating Tuesday and adding to investor concern that big social-media sites are entering a slump after Facebook Inc. and Twitter Inc. also posted slowing growth.
For the parent of Snapchat, the 2% drop in daily users to about 188 million in the second quarter marked the first such slip since it was founded in 2011, and executives indicated that the near term could be bumpy as well. That guidance was offset by an announcement that prominent...