I don't recommend anyone to use web based proxy because it's most-likely backdoored
with Java Script hook up, which track you and possibly able to compromise your data, accounts, information.
On topic, there is no need of search engine proxy, really, as @1337
said, duckduckgo does't even have your IP in database logs, so what's the reason of creating proxy at first place?
if you really want to hide your IP, use VPN.