Okay, let's lay down some guidelines here. Just so we can make sure we understand what's being appropriate, and what's totally inappropriate:
1) It's okay to occasionally reply to somebody that you follow on twitter.
2) It's a bit weird if they're 20 years younger than you, but it's still okay.
3) It's not okay to add them on facebook and send them messages about how they're such a wonderful person. Constantly.
4) It's not okay to send all their friends tweets and follow them all and intrude on all their online conversations.
5) It's not okay to reply to every single tweet they post with some kind of comment which you hope will result in a converstaion.
6) It's not okay to send them direct messages four times a day.
7) It's not okay to try and arrange a time to meet up with them offline.
8) It's not okay to tell them all your problems, they don't care.
Okay. I'm glad we cleared that up. Now, having learnt that little lesson, get on with your life and stop stalking.