Facebook’s user growth faltered in the latest quarter, the first stagnation in the social network’s history, stoking concern that Meta Platforms Inc.’s flagship product and core advertising moneymaker has plateaued after years of consistent gains.

The company also gave a disappointing sales forecast for the current period, and chief executive officer Mark Zuckerberg acknowledged that Meta is facing serious competition for user time and attention, particularly from viral video-sharing app TikTok. The dour outlook and stalled user momentum sent shares down as much as 24% in extended trading, a striking decline for a stock that has posted gains in every year but one since its 2012 IPO.

Zuckerberg said Meta’s rival to TikTok, Reels, is growing quickly, but monetization has been slow, and he asked investors for patience as the product ramps up.