According to the founder, they have been profitable since 2014.
Anecdotally, I've been seeing more and more success getting friends to switch over to DDG. This feels like early mass-adoption. It's rather exciting.
Well, except for chrome using their near monopoly on search to shove a browser in your face that further cements their place in search. and bundling it with the OS on mobile.
That's not a stable situation. The EU forced Microsoft / IE to unbundle - Google's day of reckoning approaches.