Add this rule to your .htaccess file to redirect visitors to the www. version of your website:
RewriteEngine OnRewriteBase /RewriteCond %{HTTP_HOST} !^www\.RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]