Just stumbled a tweet from SRC Apps which states that “Swapchat app for Windows Phone pulled off from Windows Phone Store after copyright complaint filed by Snapchat”. It has removed from Windows Phone Store and is not longer available and does not produces any results if you search for it.
For your information, Swapchat is the unofficial client for Snapchat app for Windows Phone. It is one of the most popular app which has more than 1300 reviews for free version. I know you like Swapchat and its reported that it works well & you can continue using the service without any problem. As long as you do not install the app or Snapchat does not change anything on their end the app will continue to work.