i tunes problem lost music

Hi,
I have a big problem. I moved my i Tunes Library to an external hard drive.
upon cleaning out my computer harddrive I found my old It tunes library folder and moved it onto my external HD.

the prompter asked me whether I wanted to cancel the transfer or replace the existing folder. I accidentally pressed replace. Now I can't find my song files.
Are they gone forever? Has anyone ben in this position before?

Any advice is appreciated.

Thanks,
M