When would you say each social app/site got popular?
A lot of people mention the release dates of apps/sites when the proliferation dates are very well more significant.
Here's a comprehensive list of each app/site that I'd say is notable/popular, or at least was, and when they got launched. I might have missed a couple of them. Since 2001:
2001: Wikipedia
2002: No launches
2003: MySpace, Friendster, Steam, LinkedIn, Skype, 4chan, Friendster
2004: Facebook, Gmail, Flickr
2005: YouTube, Reddit, Google maps
2006: Twitter, Roblox
2007: Tumblr, Hulu
2008: 9Gag, Spotify, Soundcloud
2009: Whatsapp
2010: Instagram, Quora, Pinterest
2011: Snapchat, Twitch, Uber, Keek, Google+
2012: Tinder
2013: Telegram, Vine
2014: Musically
2015: Discord
2016-2017: No launches, except games like pokemon go and fortnite
2018: Tiktok
2019-present: ChatGPT launched in 2022, alongside many AI chatbots in 2023, and stuff like Threads and Bluesky.