How to make more people know about DuckDuckGo search engine?
Well, I found out about your search engine on www.angel.co website, however I still think that most users did not heard about it yet.
If you encourage users (promo video) to use your browser, you can bring more users.
a) I think one way would be to donate some percentage of Ads earnings to charity funds (children and others). This would encourage users to use DuckDuckGo browser more. Since part of funds is going to charity, most of people would support it by using your browser.
b) When user sets DuckDuckGo as a default search engine, DuckDuckGo donates to charity some amount (it can be also part of company Ads earnings).
c) actually, this can be ongoing company policy. You search, we donate :)
In promo video (cartoon or real video), you can show features of DuckDuckGo search engine, how it improves user experience, benefits.
In video we can also mention this search and donate feature.
Now, to make this action become popular and viral, you can inform major sites like www.huffingtonpost.com who may find this action interesting and will likely spread the news.