Google Proxy Hacking
So if a site is not coming up in Google’s SERP, don’t jump to conclusion than the site is banned. Google does not ignore proxies and that has caused some issues.
It is basically a black hat trick that has been around for a while that allows third parties to effect your Google’s SERP and make your site disappear completely from Google for a period of time. Dan Thies explains this in detail in his article “Google Proxy Hacking: How A Third Party Can Remove Your Site From Google SERPs“.