The top tier is, essentially, Facebook, Instagram, Youtube and TikTok. These are used by literally billions of people; with the exception of China, virtually ev

The top tier is, essentially, Facebook, Instagram, Youtube and TikTok. These are used by literally billions of people; with the exception of China, virtually everyone on earth is exposed to them fairly directly. (Also Telegram and WhatsApp are a borderline case; they have the users, and they have social-network-like features, but most of the users are likely not _using_ the social-network-like features; they just use them as messaging apps). The second tier is things like Snapchat, Twitter, LinkedIn, Reddit, Pinterest, Quora; these are in the 300-600 million user range, so they're big, but you don't have the same sort of universal exposure.