What must I do to rank up? Do I need to play multi-player games? I've already played a hundred single player games.

Try to earn points. You can earn points by completing achievements. Achievements can be found by viewing a person's profile and then clicking on achievements. You can also earn points from winning games.

You can get the stars in Single player levels to get points;
to get more points-you need to play multiplayer games-which are ranked.
Like DanWL says there are achievements which will give you points, but playing more games and winning them are easier way to rank up.

also a good idea is to turn off any programs that will prevents add from being shown on the website so you won't get decreased experience after winning games because of that

https://www.warlight.net/wiki/Points