This challenge post page definitely indicates the already expired date of June 15, but the timeline along the top of the house app challenge website (http://www.congressionalappchallenge.us/) seems to show the results being announced June 18 (or possibly another event after the announcing of the results). What's more is that the twitter feed along the side of the same page shows that representatives Tulsi Gabbard and Suzanne Bonamici have already announced, and presented awards to, the winners in their districts on June 6 and June 4, respectively. I myself have not received any other form of notification of the winners in my district. I'm hoping an administrator can respond to this thread soon to clear up some of this confusion.
I just sent an email to one of my district's representatives about an exact date. It may be different for each district, but I'll let you guys know when I get a response. My district representative has been pretty awesome about getting back to me with information about all of this stuff within the same day.
Waiting on the results of this contest have been the most stressful part so far xD
The Members are in the process of completing their judging. We have asked that the materials for each district winner be submitted no later than June 30. We are in the process of setting up a winners site which will be put up at studentappchallenge.house.gov.