If it were possible for people in Panem to use the internet/computers, would your character have a facebook?
Mel would probably have one, though she would have to stop using it after she joined the railway. However, before that (and I guess pre-reaping of Donta), she would probably be the kind of person to like just about everything people said, and she would be that person who comments on all her friends' pictures to say how pretty they are. I can also see her having like 10 conversations going on at a time and taking lots of random quizzes and writing sweet messages on all of her friends' walls.
April would post tons of pictures of herself and probably have a different profile picture every day. She would be friends with everyone she's ever had a conversation with, and probably some people she's never talked to but recognizes. Heck, the girl would probably have some friends she didn't even know, if they sent her a request. She would update her status daily, usually about whatever she was doing with her friends, and all of April's posts would probably be written with way more letters than necessary likeee thiiiissss. And she'd probably use tons of smilies and exclamation points!!! Like Mel, she'd also be having tons of conversations going at the same time, but they would all be extremely superficial, probably her and her friends gossiping.