Facebook doesn't even use PHP anymore, they switch to their own implementation of PHP called Hack to runs on HHVM. So no, they don't use PHP per se for anything this days.
They're very much using PHP (the language) ...they just made their own runtime. They still sit down and write PHP. They don't sit down and write HHVM code.
That's like saying a company no longer uses Ruby because they use JRuby now.
http://www.infoq.com/interviews/adams-php-facebook