Search users with custom meta data

try :

$users = new WP_User_Query(array(
    's' => $yoursearchquery,
    'meta_query' => array(
        'relation' => 'OR',
        array(
            'key' => 'billing_last_name',
            'value' => $yoursearchquery,
            'compare' => 'LIKE'
        ),
        array(
            'key' => 'billing_first_name',
            'value' => $yoursearchquery,
            'compare' => 'LIKE'
        )
    )
));