For the social media companies, she said, increasing connections translates to more advertising revenue — estimated at more than $40 billion industrywide in 2020. In contrast, static social network platforms have already passed their fast-growing phase, and users generally have a stable number of friendship ties. Xie said she would consider Facebook a static social network for most of its users, while TikTok and Reddit are evolving networks. “Similarity matters a lot when strangers choose to become friends in an online social network. For social media users looking to start friendships, Xie said similarities play an important part.