HELP! Data is lost

Hello,
I recently bought a 1TB WD external hard drive. I transferred my life from my old 750gb external and recent items from my macbook pro to this new external. Some how everything is GONE! I have searched and searched and searched again and still there is nothing!!! I did not delete these files and I would have known if I did because it would have took a while since there was probably around 650gb of files on there. I NEED all of my files, can anyone help me try to find them or restore or recover somehow?! Please