Honestly, It means they are probably not interested. Don't take it personally because it probably isn't. I've had guys message me on here a couple times but I never replied because sometimes they are older than what I'm looking for or I see that I have nothing in common with them. Sometimes messaging back just isn't worth it because although they may be a real nice people, I just don't want the mess of wasting my time or leading them on. Just stay positive and keep messaging others because just like meeting people in person it's hard to meet the right ones and it takes time to find someone you're compatible with.