Adding items to credits using the 'toolbox_credits' hook

I can see in the footer of this theme:

<?php do_action( 'toolbox_credits' ); ?>

So I was trying to add items as follows in my child theme’s functions.php:

function ch_credits() {
	return '<a href="http://chesshive.com/">ChessHive &copy; 2009-'.date("Y").'. A project of <a href="http://deuts.net/">Deuts.NET</a>.' ;
}
add_action('toolbox_credits','ch_credits');

But really, nothing is happening.

http://wordpress.org/extend/plugins/toolbox/