this girl never responded to my message on facebook?

[Tom]

Honestly man it sounds like a situation where your brain is making this into a bigger deal than it really is. I feel the same way as you that people should respond to a message if they see it and I tend to feel like something is up when they dont. But its really not a big deal, nothing is wrong, she probably was in the middle of doing something when she saw your message and just got side tracked and forgot about it.

Seeing as she came up to you in person and made a point of talking to you I would say everything is fine. Here's a pretty cool page about contacting girls which lets you in on how their minds work when it comes to things like texting and facebook messages and things like that.
http://datingdominance.com/category/contacting-girls/

Hope this helps you out my man! Good luck!