Believe it or not, Notepad++ does not support the use of linebreaks in regular expressions for its “find” feature—it’s regular expression support is quite weak actually.
But if you don’t use regular expressions often enough to look for an alternative to Notepad++, here’s a trick to get around the limitation.
Open the find dialog and select the “Replace” tab. Change the Search mode to “Extended”. Now in the “Find what” field enter “\r\n” and in the “Replace with” field enter “__RN__” and click “Replace All”. Now all the linebreaks in your file will be replaced __RN__ so you can use this string in your regular expession in place of the \r\n. When you’re done, use the same method to convert __RN__ back to \r\n.
I used this method to identify multiple linebreaks in an .srt subtitles file and replace them with a single linebreak.