$search_string= $args = array( 'meta_query' => array( 'relation' => 'OR', array( 'key' => 'firstname', 'value' => $search_string, 'compare' => 'LIKE' ), array( 'key' => 'nickname', 'value' => $search_string, 'compare' => 'LIKE' ) ) ); $users = get_users($args);