Thorough documentation of the phenomenon:

https://en.m.wikipedia.org/wiki/Sasaeng_fan

According to estimates given by celebrity managers to Korean media, popular Korean celebrities "have between 500 to 1,000 sasaeng fans" and are actively followed by about 100 sasaeng fans every day. Sasaeng fans are generally said to be females aged 17 to 22 years old who are driven to commit acts of, in some cases, borderline criminal behavior in order to get the attention of celebrities. These acts may include but are not limited to: seeking out celebrities at their dorms or homes, stealing their personal belongings or information, harassing their family members, and sending idols inappropriate "gifts" such as lingerie.

Two recent examples involving the popular group BTS:

https://www.kpopmap.com/girl-tries-to-force-a-kiss-on-bts-suga-and-another-doesnt-wear-any-pants-to-get-bts-attention/