Change your region to a more populated area in order to get matched in Ranked play.
So for unranked play you can change your filter to worldwide and find matches anywhere, but for ranked there is no in game option to change your region. So if you are in a lowly populated part of the world you will find it very hard to find a match.
To fix this you can change your Steam download region to wherever you want to play in. Obviously it would be better if you picked a region closeby but is far more populated.
If you can't figure out how to do this I've made a video.