Nintendo announced earlier this year that they're teaming up with DeNA to create (at least) five mobile games to launch over the course of the next year and a half, and the first game will launch later this year. We haven't seen any of these games yet, as Pokémon GO is not part of the DeNA venture, but we should have our first news very soon.
We learned back in August that Nintendo and DeNA were working on announcement plans, and an industry insider recently stated that we can expect news soon. Now we're hearing that message from DeNA as well, as CEO Shintaro Asako recently said the following at Games Beat: "Soon, we should be able to announce the game." We'll be on the lookout for the big reveal sometime soon.