DS (year 12) has been tutoring a year 9 girl for about a year. He told me that someone stole his phone without his knowledge during sixth form today and started mass sending sexual messages to all the girls in his contacts on snapchat. One of the people that was messaged is the year 9 girl DS is tutoring saying something along the lines of "Do you want to hook up I'm horny." DS was friends with the person before the incident and the person did it as a "joke". I encouraged DS to inform his school about this situation but he is refusing to do so as he doesn't want to be seen as a snitch by others and is saying his friend did a joke that crossed the line. What should I do? What action will the sixth form take against the pupil likely if informed?