WordPress at a glance
action is not described

ms_site_not_found action-hook . WP 3.9.0

Fires when a network can be determined but a site cannot.

At the time of this action, the only recourse is to redirect somewhere and exit. If you want to declare a particular site, do so earlier.

Usage

add_action( 'ms_site_not_found', 'action_function_name_481', 10, 3 );
function action_function_name_481( $current_site, $domain, $path ){
	// action...
}
$current_site(object)
The network that had been determined.
$domain(string)
The domain used to search for a site.
$path(string)
The path used to search for a site.

Where the hook is called

ms_load_current_site_and_network()
wp-includes/ms-load.php 400
do_action( 'ms_site_not_found', $current_site, $domain, $path );

Where the hook is used (in WP core)

Does not used.