If after updating OS X to Mavericks, your local Apache setup stopped returning the websites that you had setup locally, then it’s highly likely that your httpd.conf has been overwritten. However, before it was overwritten the Mavericks setup created a backup of the httpd.conf file, httpd.conf.pre-update, in /private/etc/apache2/ folder. You can use diff tools to find out the difference between the new and old httpd.conf files. Most likely, the inclusion of httpd-vhost.conf file must have been commented out, so uncomment that (along with any other changes that you might have had in the older httpd.conf file).

Reference: Quick Tip: Getting Apache Up And Running After Updating To Osx Mavericks (10.9)