Finding citeable statistics I am in the process of writing a literature review as part of an application for a master's course and would like to cite Facebook as being the world's most active/ popular social media (or 2nd or 3rd happy with it so long as it is accurate).
Googling 'worlds most active social network' brings back multiple results from a variety of websites but no official press release of numbers from Facebook, or what I can see quotable articles. When faced with a problem like this:

Is there an advised, reliable way to find and cite the data? Only from a certain list of websites?
Is this fact so universal that it need not be cited?

Thanks in advance
Is there an advised, reliable way to find and cite the data? Only from
a certain list of websites?

A quick one would be Google Dataset Search.
A more 'community'-led one would be DataCite whose stated aim is to provide DOIs for research datasets.
If you need data owned by the public sector (governmental data), so-called Open Data Portals are the way to go. For instance, this one by the EU.
However, the whole area of research data management (RDM) remains underdeveloped. Thus, do not be surprised if you do not find what you are looking for.