Ghosts multiplayer is set to be revealed on 14th of August, just 2 weeks from now. The event is sponsored by Microsoft, which means we'll most likely see Xbox One multiplayer footage.
To date every Call of Duty game since Modern Warfare 2 has had their first multiplayer footage teased or fully revealed by late July or early August - and the game itself playable a few weeks later by fans or selected members of the press. The only exception was MW3, which was revealed early September during the massive Call of Duty XP event.
It's been confirmed that the "GameStop Expo" will be held on 28th of August in Las Vegas and COD Ghosts will be playable there. The press release states that you can get "hands-on experience" with the game, but no official confirmation has been given if the game demo will be multiplayer based or not. It's likely that the multiplayer will be playable at the Gamescom Cologne event during August, just like with last year's Black Ops II.