I say **** 'em if they don't reply and dock 'em off your friend list
You know, certain people have certain things they have to do. What if they're having a lot of school work to do? What if their jobs are stressful and they're relaxing? What if you message them at the wrong time (ie, when they are about to have dinner)?
There are a lot of 'what ifs' here, you can't just assume they're ignoring you and start hating their guts for no reason.
If they're not being as responsive as you'd like, just say something like "sorry, I suppose you're busy" or "I'm sorry if you're busy", or even ask them directly if they are busy or not.
Or you can always ask if they've lost interest and why. If the reasons are somewhat valid, then try to work on your flaws in order to become more interesting as an individual and thus have more things to talk about. It's hard to have anything to talk about when your days are dull and pointless, which is why we have to get out there and enjoy the time we're given.