My daughter is now 17 BUT we have been going through the older boy stage since she was 13.
Nothing we did helped. She just got smarter then us... and we did everything we thought we could. But I would in fact inform this 17 year old that she is underage... and he is playing with fire. I am a single mom and had to deal with a 24 year old two months ago who was leaving notes on my daughters car while she was in school. He didn't much listen to me. BUT I did have a male friend go talk to him. Seems he thought I didn't matter but the male friend took care of it. There have been no more notes and I also blocked his number from her phone. He can't text her. Nor can she text him. But with Facebook and Myspace and twitter and all the other internet things out there it is just nearly impossible unless you are by her side 100% of the time. If you pay for her phone then I would put limits on it. She is 13. Take it at 8pm at night. Don't return it till the next day when she will need it so you can reach her. A few weeks of that and that just might get her attention. You also want to contact your phone provider and let them know that YOU and you only are to make any changes to your account. My daughter called sprint herself and they let her make changes regarding who was blocked etc.
I wish I had better advice. But as I have learned all too well kids find ways to talk to people because there are so many outlets. But I would give this boy warning about having ANY contact with her. You can also have a local police officer pay him a visit... to make him see you ARE serious........ I wish you luck dear.

I have a 16 year old daughter and thankfully shes not the type whose world revolves around boys entirely, but she has several friends who I have watched go through these scenarios, and my advice would be a little different and I will explain why. You see, some girls like drama and ticking their parents off or getting away with something you don't approve of. It is enticing to her to push those buttons, so if you don't let something bother you, or at least you don't let her see that it bothers you, it suddenly isn't so interesting to her.
Now, this might be something to consider, invite the boy over for dinner with all of you. You could even invite several of her friends, maybe even some of her more immature acting 13 -year-old friends, so the boy loses interest. If your daughter sees you not being bothered by the friendship, you may find her interest in him drifting away....also, while he is there, at 17, you could ask him about his future plans, college etc....that might plant some seeds to your daughter who is yet to experience even high school that his plans aren't as fairy tale as what is inside her head.

My daughter has a friend who has been forbidden to be with a boy to the point the police have been involved, and every time she wants some attention from her parents, she runs off and finds that boy and irritates the snot out of her parents. One day, when the girl had run away to him (and I do mean run away, she packed and left) they told her okay, packed up her stuff and told her to GO.....she came back in no time at all and that boy's flaws suddenly became very apparent to the girl and it is no longer a problem for them....thank goodness she wasn't pregnant before all was said and done, but anyways you get the idea.

Frankly, I would have to ask what on earth a 17 -year-old boy wants with a girl so young? Most 17 -year-old's I know are looking at 25 -year-old women. I don't blame you for being worried one bit. Remember to keep the curfew limits and rules 13 year old appropriate, that gets old to a 17 -year-old real fast.

As far as you dropping her off to see her friends, I know she seems to old to be doing this, but before she goes over to a friend's house, you need to speak to the parents of that home and let them know your daughter is coming over, make sure that isn't a problem for whatever is going on with them at the time and make sure you are all on the same page with what the girls (or boys) are doing, and who might be there. The one time I didn't do this, it turned in to a big problem with another parent returning my daughter home after being found with a car full of boys sneaking off to her dad's house which was empty because he was out of town, and each girl had told their parent they were staying at the other's house that night....boy, I had to lay in bed with the flu just for one day and wham, she takes advantage of my not feeling up to checking in with the other parents and it came back to haunt me....and were talking about a pretty responsible kid here, so always be checking, you'll find the other parents appreciate it and may feel more secure to check with you when their kids are coming to your home.

What good can come out of them seeing each other?
I would just say that he's too old to hang out with.