Duckduckgo is one of the challengable search engine in the internet against google. However this search engine has never meet any good rank in the internet to challenge google even though duckduckgo is getting some good users daily. Internet is independent mass media in which anyone can share their thoughts and surf their wants but most of the search engine including google, yahoo, bing etc track the IP address along with the search keyword but the duckduckgo offers complete indepentence to the internet users to surf anything that they wanted without tracking and IP address or the searching keyword. This search engine was ranked 1867( may vary) in the internet based on the alexa traffic rank. Because of the independance issues on the email and searches google has faced many problems. There was statement was came that the emails and nails that in the gmail is handled by more than one checkers because for the safety measures this statement created a big question about the privacy of the internet users.
Using this statement duckduckgo was came into the internet world with an offer that using this search engine will not track any of the privacy searches or keywords. Mainly in blogs and sites the search engine provides the traffic sources and searching keyword that used by the visitors to came into the site but duckduckgo's owner Gabreal Wayinburg announced that their search engine will not give any information to the webmasters by considering the privacy of the searching. But google is in the top of the site even though this statement came into some issues. Google has ranked 2 in the alexa traffic rank which is something that in top which an another site can't replace it. All the best.
(all this information regarding this search engine is get from different reference sources)