To remove empty comments form Visual Studio 2012 use this regular expression:

^(?([^\r\n])\s)*//\r?$

and replace all the matches with nothing. Just make sure you are only searching in *.cs files. Because this can mess up other files, like JavaScript

Apparently whitespace is matched by (?([^\r\n])\s) in VS search and replace tool. While \s is a white space including new line and carriage return character

Reference to Visual Studio 2012 regular expression search is here: http://msdn.microsoft.com/en-us/library/2k3te2cs.aspx