Proxies are quickly blacklisted.
There are entire companies that occupy themselves with the collection of proxies, tor exit nodes, vpn adresses ,botnets etc etc.
What they then do is sell them to other companies which block those adresses as an anti cheating system.
Ever wondered why adf.ly bots dont work
Basically you should scan your own and use them directly.
Google also keeps track of the previously mentioned addresses.
Footnote: hidemyass sells your ass, never trust them.