Unfortunately, this is not an uncommon problem in the school setting:
http://myfox8.com/2017/08/06/high-school-teacher-accused-of-sexually-molesting-8-students/
Sadly, there are sick people out there. They will find a way to gain access. That said, most "grown men" are not sick people. Please don't lead your teenage girls to believe they are. But also, be sensible, and encourage them not to be alone with any grown men-- in cars, at hotels, or behind any closed doors.
Our girls are not victims. They should be able to understand when a text about "good first touch" becomes about something other than their feet.
They should also be empowered to speak up if it does. And that, fellow parents, is also up to us.