That is a pretty tough question. I share your concerns, because I too have two daughters. So I will give you my personal opinion, if you don't mind.
Of course, we should always know what our daughters are up to and who their friends are. Communication is not always easy, depending on the age of the children, but parents must be aware of what their daughters are doing. That is the reality of it. It all boils down to communicating. That is all I can tell you, but that is my own personal opinion.