$re = '/(?:^GROUPS:\h*\["(?=[^][]*])|\G(?!^),\h*")(?<name>[^:]+):(?<id>\d+)"/m';
$str = 'GROUPS: ["group1:44343", "group2:23324", "group3:66567"]
USERS: ["user1:44343", "user2:23324", "user3:66567"]';
preg_match_all($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