Database Design for Large Social Media Websites

I have read creating tables for each user is not at all recommended (Mentioned here).

So, how do websites like Instagram, Facebook keep records for followers/friends for each user. For example, some celebrities have more than 100 million followers on Instagram. Do these websites keep a single table for followers/friends like - <row_id> , <user_id> , <follower_user_id> and partition the table in multiple smaller tables using the <user_id> column?