Social Media Users 2020
Facebook 2,701,000,000
YouTube 2,000,000,000
WhatsApp 2,000,000,000
Messenger 1,300,000,000
WeChat 1,203,000,000
Instagram 1,082,000,000
TikTok 800,000,000
QQ 691,000,000
Sina Weibo 550,000,000
Qzone 517,000,000
Reddit 430,000,000
Kuaishou 400,000,000
Snapchat 397,000,000
Pinterest 367,000,000
Twitter 326,000,000
Facebook has more reports because they by far have more worldwide users. We here a lot about Twitter, but in terms of market share it is far down the list.
I put YouTube in a different category as it is really a video distribution platform. They also police their stuff and you have to go through a hoop to view anything deemed 18 plus. There are at least two other service similar to YouTube. One of them, DailyMotion will show stuff YouTube will not, but they don’t allow actual porn.
Using your numbers for users and the articles numbers for reports:
Facebook has a report rate of 0.7515%
TikTok has a report rate of 0.0028%
I realize there are many factors involved, but that’s still quite a disparity.