Don't give up Shadow Rogue! Although I've almost never had the kind of experiences you've described, the few times I did, it was frustrating. I'd say just continue what you're doing until you find the right players to have fun with. It sounds to me that you're doing the right thing by at least waiting to see what's happening between some characters before jumping into the conversations. I can only guess that maybe the times you've been ignored, either the other players were new/not experienced, or for whatever reason, did not notice your character or thought their characters would ignore yours in the particular situation. A tell or something would have been nice of them if that was the case.
It's also a good idea to check the current descriptions too if you have a chance first. Some of us put anything currently notable about appearance at the top. I've many times been in the middle of a stressful rp situation only to have someone waltz up with a cheery greeting, completely out of place for most characters if they'd known what was going on first. In those situations, I always attempt to let the other player know the circumstances usually in my next line. For example; /me continues weeping, drawing knees upward toward her chest while hands cover her eyes and the stranger's greeting goes unnoticed. This, to me, is not a rebuff meaning your character should go away, but simply an invitation for the character to do what they may in that situation now that they know better what is occurring.
Like Rigwyn pointed out, I've all too often been too slow in typing a response only to have the other character disappear before I can hit the enter key. I have also come across situations where some appear to be talking on a private channel and ignored what was going on around them, or were so engrossed in training they never notice a hello. Just don't let it discourage you. Many seem to have their own ways of playing so just keep looking for ones you fit in with. I'm sure they're here from what you've described of your rp style.
