Simple apache proxy not working

The default vhost (which serves content from /var/www, where the "It works" page lives) is getting the requests.

It's loading first, and you haven't specified a ServerName for your new vhost, so the "default" vhost will get every request. Run apache2ctl -S - it will show you how it's assigning requests.

If you don't want to use the default site, disable it with a2dissite default, then restart Apache - requests will then be sent to your new proxying <VirtualHost>.

Additionally, your trailing slashes should always match when proxying. Add them at the end:

ProxyPass / http://www.google.de/
ProxyPassReverse / http://www.google.de/