I don't know what TikTok is but Reddit and Hacker News are not "social media", they are just discussion forums.
Not all online communities are social media. The key feature of social media is that you chose WHO to follow instead of WHAT to follow. That's the part that makes it "social", because you create a graph of social connections as a fundamental part of being a user of the site. This is, not incidentally, what makes social media extremely attractive to advertisers.
> Social media are interactive digital channels that facilitate the creation and sharing of information, ideas, interests, and other forms of expression through virtual communities and networks.
Check.
> Social media are interactive Web 2.0 Internet-based applications.
Yes I think so.
> User-generated content—such as text posts or comments, digital photos or videos, and data generated through all online interactions—is the lifeblood of social media.
Definitely true of all three.
> Users create service-specific profiles for the website or app that are designed and maintained by the social media organization.
Check.
> Social media helps the development of online social networks by connecting a user's profile with those of other individuals or groups.
Not all online communities are social media. The key feature of social media is that you chose WHO to follow instead of WHAT to follow. That's the part that makes it "social", because you create a graph of social connections as a fundamental part of being a user of the site. This is, not incidentally, what makes social media extremely attractive to advertisers.