$re = '/\sNew User:\s(.+?_user)\sfunction:\s(auditor|auditor2)\s/s';
$str = 'blablabla bla bla blabla New User: John_user function: auditor blablablablabl bla blab New User: Do_user function: auditor2 blablabl blablb...';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php