Is C++ worth learning for webapps? I know python and it works well, so would it even be worth it to learn c++?

Same answer as here.

C and C++ share a lot of the same community, and are often employed to do very simular things.

yes of course. Try for it

Use PHP for webapps. It is a derivative of C++, so learn C++ first, and apply the object-oriented principles you learn there to your PHP code.

I already know PHP and HACK the new programming language from facebook.