OK -calm down -she's 13 and into puberty! The hormones are raging, and you need to CALMLY sit down and talk to her IN GRAPHIC DETAIL about sex, sexual relationships, your expectations of her, how to keep herself safe, etc. Also, PLEASE seriously discuss the ramifications of what she posts on ANY social media site -Twitter, FB, whatever. She may think they're "private" but they're not! Hammer home that anything she puts out there CAN come back to haunt her. Let her know all it takes is posting something like that and having someone else at her school see it and start telling people, and before she knows it people are making fun of her and saying things about her that aren't true and that she'll hate.
At their age, it's all about those first feelings of arousal. I know it makes you want to puke, but this is the terminology kids that age use. He is certainly of the age when even looking at a girl he likes will give him a "boner"! Tell her it's not really nice for her to be talking about this type of thing with him, and that at their age, they should keep their bodily functions to themselves. This will let her know more where you stand. Just make sure their visits are supervised at this age!
We live in a digital age, and you can "ground" her from electronics for a little while, but you can't keep her away from them. You need to teach her how to use them responsibly. There are also a number of programs that aren't very expensive per month that you can use to monitor your kids' texts, social media sites and email. The cool thing about the new ones is that they're not total spy ware where you see all of their stuff and they hate it, but you get to flag certain terminology (like boner), phrases, etc. and the messages, posts and texts come to you first before going out or going to her -so you can approve or disapprove of them and talk to her about it. I know one is called CoolYou. You could make using this a condition of her having a cell, using Facebook, etc.
She's still really young, but overreacting will only hurt. Have a serious talk and then have some more. Have talks about relationships, romance, love, sex and all of it frequently throughout her adolescence!