Maybe they are busy or even are not near the computer? If you worry about it, you could ask people, if they are ignoring you, or it's mistake?

ok dear , try that next time don't say hello change it ,

I may understand why they do that. I do not like to chat with someone there's no word on their profile or their sex/age is unmentioned. Although you and I haven't made friends yet, you can see my sex/age/words on my profile. But I can't see yours. Do you guess how I feel if you try to chat with me? They would feel like that.

Keep silence if possible.Then let she or he say.if she or he still make no sound.Perhaps she or he don't like you even hate you this moment. you should meet she or he next time.just dating she or he then.But if you're a shameless man.you can try and try again until she or he make a response to you.

Maybe the internet link is down, or the person did not receive the message, many other un-explainable situation. Move on to know others... Don't think so much in-between the lines...