What does 被圈粉 (bei quan fen) mean?
圈粉 refers to someone using various methods to expand one's social network following such as on Youtube, Instagram or Weibo. Afterall, in this day and age, the more fans or followers that one has on their social media, the more influence or power they have. It is now recognised as a form of capital.
Therefore, 被圈粉 is then used when you like someone, and use all the ways and means to support that person -- similar to how a fan supports their idols.