Very difficult area this.
My step daughter is only just 13 and hasn't started developing visibly yet, other than gaining height rapidly! A week or so back we stumbled across a letter under her pillow saying how she liked a particular boy at school, and since then there have been emails and possibly SMS's from girlfriends whom we believe are liaising between them. (there was an email with a photo attachment). My wife and I are not letting on that we know about this.
I encourage my wife to try and develop a friendly rapport with her daughter (as I do myself) and not to be quick to criticise her (which she is). We have previously set the scene with her daughter that we have brought her here to live with us, so that she can be with her Mother, have a father, and significantly to enable her to get a better education and prepare for life than would have been the case way out in the "outback".
The daughter is progressing reasonably well at school, though seems to be a bit of a "dreamer" when at home, preferring to listen to music (South Korean girl and boy bands), play on the computer (mostly listening to YouTube), sketch clothing designs, or watch TV.
We have gently intimated that education should come before boys or other things, - they can come later, and talked to her about peer pressure and some possible scenarios, (involving such things as m/bike helmets, smoking and drinking) and are hoping that she will share/talk to us or her Mum about things that evolve, though personally I'm not convinced she will. [-o<
I see the challenge as how to create a sharing of information and experiences culture/rapport with her without her feeling shy or threatened, when she seems to naturally want to play her cards close to her chest.