Why didn't my friend answer me on Facebook?

[Sunshine on a Cloudy Day]

So I innocently asked my friend (girl a) from my lab class this past semester about the whereabouts of a mutual friend of ours (girl b) since this mutual friend of ours gave me her number.

I have tried to get ahold of girl b twice since the last class (last one forever), and she hasn't been picking up and she hasn't been on facebook since december 1st.

After I asked girl a about girl b's whereabouts, facebook said that girl a just "saw" the message but didnt respond!

I do not have girl a's number and I probably won't see her again unless we hang out because my college is pretty big.

I found it pretty rude how girl A did not answer me.

What's wrong with asking someone about someone else's whereabouts?