After getting a random "hi" from another member, I decided then to do the same. I usually say "Just thought I'd say HI! Hope you don't mind and I apoligise if you do." And just leave it at that. If they want to reply great, if not I don't mind and understand. It doesn't always work but hey.
I don't mind if others want to randomly chat to me, I actually welcome it. So, if any of you want to chat, sure to say "Hi"