To stop sharing a particular file or folder, you can right-click it from the Library window. For deleted files, you will need a file recovery utility. http://www.gnutellaforums.com/showthread.php?t=49851

For free ones, Restoration (click on link) seems to be the best. But don't save back onto the same partition you had your erased files on, else it will write over the other missing files. Also stop writing to that partition.