use File::Find to recurse through subdirectories, open to open files and readline to read lines from the file. Assuming your code isn't particularly obfuscated, you can almost certainly use sub\s+user_method to match your subroutine.

use File::Find;

find( \&wanted, '.' );
sub wanted {
  open my $fh, $_ or die $!;
  local $/;
  my $file_contents = <$fh>;
  if( $file_contents =~ /sub\s+user_method/ )
  {
    print "Matched $_!\n";
  }
}
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Note that I undefined $/ so that my readline reads the entire contents of the file in to one variable. This is because your method declaration might contain an embedded new line. This method is slightly less efficient than reading line by line, but for something of this nature it hardly matters, as perl modules are rarely more than a couple of hundred kilobyes.


Update: Fixed my broken closing code tag.