Considering the magnitude of data available on Rapidshare servers, it always makes sense for Rapidshare to provide a basic search engine to look for a particular file. Since, the data uploaded is meant to be private, unless the exact URL of the uploaded file is shared by the owner, Rapidshare has not provided such options.
Nevertheless, other people have come up with their own search engines to search for files on Rapidshare. Some time back I had shared 21 Ways to Search For Rapidshare Files. All of these are online web services/tools.
In case you want an easier option, Rapidshare search Addon for Firefox makes Rapidshare search easy by integrating search facility for download links right beside your browser’s address bar. This plugin uses Google to search for Rapidshare files links. After installing this addon, you get a new search option where you normally search the web with Google (top right corner of your firefox window).