Here is a quick thing, someone can do something better when we get closer to the con.
Starting from those stairs between South Hall and West Hall where the really large cosplay gatherings (final fantasy, etc.) take place.
Just take the bridge from the second level across Pico Blvd. Then look to your left and look for some stairs down. Once you take the stairs, the gathering will likely be just in front of you. This is about where it was last year. If not, try turning around and walking toward the front of the convention center.