You're the PM for Facebook. There's been a significant drop in user engagement over the past 10 days. How would you investigate the cause and what steps would you take to address it?

My first step would be to segment the engagement drop to pinpoint the scope: Is it affecting specific regions, demographics, or device types? Simultaneously, I'd investigate technical issues like bugs, broken user flows, or recent code deployments. If no technical cause is found, I'd explore external factors: Has a competitor launched a compelling new feature? Are there any significant marketing campaigns or political events influencing user behavior? Is there negative press surrounding Facebook? By systematically analyzing these potential causes, I'd aim to identify the root issue and then formulate targeted solutions.