You can find your friends either by looking in the Lobby or by looking in the Information pane.
In the Lobby, click on the Friends tab to show all of your friends who are online [similar to finding players online].
In the Information pane, click on the Players tab, then click on the Friends tab. This displays a list of all your designated friends. To view only your friends who are online, use the drop-down list and select Online Friends.
To display a friend's player information, click on the friend's picture or name.