Should I pursue her ? Or Should I let go ?

There is a girl whom I like very much.. I met her in a short class I attended.. I was completely blown over since the first meeting... Since then we have been chatting very nicely on FB... finally I asked her if we could meet up and she said yes and suggested a day too.. then she stopped replying on chat for the next few days ( I could see her online )... then again when I decided to try for one more time she replied saying that her chat was malfunctioning and once again suggested another day.. then again she disappeared before we could confirm anything... Now she has again stopped answering..
what should I understand by this ? If she wanted she could easily have said No initially by stating an excuse that she was busy or something...
Why to keep saying yes and then mysteriously disappearing ? I am more distressed because I have feelings for this girl which I have never felt for anybody else... please give me your opinion...