$re = '/(?m)^(?=.*(?:\r?\n(?!\r?\n).*)*?\bNew-York\b)(?=.*(?:\r?\n(?!\r?\n).*)*?\bBerlin\b).*(?:\r?\n(?!\r?\n).*)*/';
$str = 'This is paragraph #1
New-York, London, Paris, Berlin
Some other text
End of paragraph
This is paragraph #2
London, Paris
End of paragraph
This is paragraph #3
New-York, Paris, Berlin
Some other text
End of paragraph
This is paragraph #4
End of paragraph
This is paragraph #5
Paris, Berlin
Some other text
End of paragraph';
preg_match_all($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