I agree with Johnnyhex, you do not want to communicate neediness, but you DO want to start raising her interest level (attraction) because right now she has 'none'. If you do not get this girl interested in you, she will continue to blow you off and send friendly messages on Facebook.
Be flirty, send cocky messages, be thrilling, mysterious, exciting, challenging. These are the traits that women can't do without. These are the traits that will get her into your bed QUICKLY. Hell, if you do it right, the 2 of you won't make it to the front door before her thongs start slipping off. Get into head and send her emotions on a roller coaster ride. She will love you for it.
"Just got your voicemail. I've been crazy busy but hopefully I'll see you out sometime soon!"
My response: let me know when so i have time to run and hide.