To find at any time another player, whether she/he is playing or not, click on the gear symbol at the top left:

Click on the human figure with the magnifying glass symbol:

You will be shown this panel.

Type the user name (or part of it) in the box indicated by the yellow arrow.

Click again on the human figure with the magnifying glass symbol:

You will get a list of all the players whose name contains the letters you entered.

Clicking on the item you are interested in, her/his profile will appear and you will be able to ask a friendship, invite her/him to your club, send a message, and so on.

If she/he is playing now, her/his image will appear in color, otherwise you will see a gray silhouette only.