[header] How to gauge the popularity of a topic online [title] Identify a canonical (preferably official) facebook page associated with the topic where applicable. [substeps] Entities that correspond to living persons or active brands, companies or other kinds of organizations are likely to have official pages. For an official page, you'll see a blue check mark (specifically, white check mark with a blue background) at the end of the name. 
Currently active large companies are highly likely to have official pages. Among individuals, currently living celebrities in movies and music are highly likely to have official pages.