Moved iTunes folder too many times!?

Hi. I want to get your advise.

I moved my whole iTunes folder onto my external hard drive to free up space on my Macintosh HD. I have done this before and only the actual mp3/avi files .etc were transferred onto my external had drive, leaving the names of the songs and all my complied iTunes folder left behind untouched.
This time though, when I moved the iTunes folder, all the song names and compilation folders have disappeared in the iTunes window.

I need to find one of the folders which was lost as it has all my favorite songs in it.

How would I go about doing this?
Which is the iTunes file which has all of the song titles and folders preferences within it?

Thanks so much again,
Josh