A.Q.
To be honest, my kids are still young and I haven't been in this situation as a mother, yet. Still, I have worked with teens in a social services setting and have a lot of experience with "Teen Thinking." What your daughter is doing is perfectly normal and age appropriate. Teens don't date the same way as we did. They do things in groups. I wouldn't worry about it. What I would do is encourage you to get to know her friends and this boy in particular. If possible, meet his parents. Treat it just as you would any of her girlfriend and let her know that it is important to you to know who she is spending time with. You can tell her all you want that she's not allowed to have a boyfriend, but if she's got feelings for this boy, there's not much you can to to change that. It's best that you let her know that you're keeping a sharp eye on her and all her "friends." And trust your insticts. If it feels wrong, don't ignore that feeling.
Good luck. I hope this helps.