(thought this might be a good place to gather ideas, as massive crowd scenes for parties, clubs etc can be challenging with the large wall of text to deal with. Feel free to add suggestions, I can collate them all as a guide when we're done)
Keyword alerts: these are really handy to set up so that if someone posts with your name, their posts will be highlighted in the colour of your choice. Worth setting up with your character name. Also try to use names in large groups so that the keyword alerts will be triggered.
Private message prompts: can often be a good idea to nudge someone in a PM that you have posted at them in the main chat, as that wall of text can be tough to scroll through!
Post length: With so many people posting, be considerate of others. Keep to the regular limits of one post - try to avoid long posts that run into 2/3 posts. With a big group, people don't have time to read extremely lengthy posts.