For Facebook contributors and readers are blended together into the same community. So it is not quite correct to call all users contributors.
People spend time on Facebook because they want to engage with the content, and advertisers pay Facebook money because they want to reach the readers. The real workforce of Facebook is all the people who are creating Facebook content. That’s closer to 800 million people (roughly their user base) than to 3,000 people (roughly their number of employees).