My finished MP-games can be found in the site map.
My or user-specific running / finished MP-games, or MP-games I'm observing can be found with the games page. Enable the checkbox near the -icon in the GameType-column and press Search and you will get the game-list restricted to MP-games.
All running / finished / observed MP-games can be found with the games page. Select "Non-Std" in the GameType-filter and you will get the game-list restricted to MP-games.
To view the managing page for a single MP-game, follow the linked -icon near the games GameType-info.