Expert Jo says:

This is a difficult dilemma and I really feel for you. I had my diary read when I was a teenager and it destroyed my trust in and respect for the person who read it, so I would strongly advise you to keep your snooping to yourself. Instead, why not bring up these topics in general over a dinner conversation? You could find an article online that talks about teenage sex and drinking, and talk to your daughter about how much it would worry you if she were doing the same. But, crucially, I would be sure to tell her that it’s very normal to want to experiment and that it’s not something for a parent to judge in their child. Keep your words to those of concern, not criticism. That way, if she does want to confide in someone in the future, it’s more likely to be you.