As of Mountain Lion and Mavericks you cant start apache off the share menu in system preferences. If you want to start it manually go the the terminal and type:
sudo apachectl start
But, if you want it to start on every launch you can add it to the launch agent by the following:
sudo launchctl load -w /System/Library/LaunchDaemons/org.apache.httpd.plist
The -w is to make it permanent. And ofcourse if you want to remove it again, just change load to unload.