Twitter help!!! I'm new user and need some answers!?

[THETRAVELER]

Sadly you can't send a DM for someone that doesn't follow you.
I don't think there's a way to know if somebody's online in a direct way.
You can know indirectly, for example, if you see them tweeting the moment you are online, then they are most probably online. So you are online, and if new tweets appear on your home and were posted like 8 seconds ago, then this person that is tweeting is most probably online right now, except if he logged off and closed twitter right after he tweeted his last tweet.


PS: There's a slight chance that celebrities will answer you tweet concerning them ( where they are mentioned ) since they get hundreds of mentions every minute. But don't lose hope =)