Index: wp-includes/ms-settings.php
===================================================================
--- wp-includes/ms-settings.php	(revision 21204)
+++ wp-includes/ms-settings.php	(working copy)
@@ -81,6 +81,9 @@
 	}
 
 	if ( ! defined( 'WP_INSTALLING' ) && is_subdomain_install() && ! is_object( $current_blog ) ) {
+
+		do_action('blog_not_found', $domain, $blogname, $current_site, $current_blog, $path );
+
 		if ( defined( 'NOBLOGREDIRECT' ) ) {
 			$destination = NOBLOGREDIRECT;
 			if ( '%siteurl%' == $destination )