This had happened quite a but in my congregation.
The girl, a pioneer, and the guy, a MS, had fooled around a few times at his house in his car in the garage. They were both teens. The story goes either the girl got a guilty conscience and fessed up or her sister saw them and told the elders herself. By the end, the girl got public reproof and the guy got df'd. I knew the guy and could tell he was remorseful. The guy got reinstated, but he slept with a non JW girl, got df'd again and hasn't returned since.
Funnily enough, the same girl got involved in another sex scandal as well. This time she slept with the son of another MS/auxiliary pioneer. They probably could've kept the secret this time, except she wound up pregnant. This time, they were both df'd.
I know one in particular of an elder's daughter had multiple boyfriends and had sexted other guys as well. I felt bad for her in particular because she was constantly held up as an example in the hall and was always under so much pressure to be perfect. The other elders covered up what she did, but I bet her father will never let her forget it.