Celebrity Engagement on Social Platforms

Imagine you're a product data scientist at Facebook. The platform is introducing a new feature called "Mentions," an app designed for celebrities to engage with their fans on Facebook. How would you evaluate the performance and effectiveness of the Mentions app? Additionally, if a celebrity starts using Mentions and increases their interaction with fans, how would you differentiate between the engagement driven by the app and the celebrity's personal initiative to engage more with their audience?