I'm not really sure that legal action can be taken against just the promotion of any illegal act. If that were the case then anyone who has ever advocated repealing any law that criminalized any action would be in trouble.
Only if the server is located within the US, actually. If it is outside the US, it is outside our jurisdiction, and the law cannot do much, if anything.
The citizenry, on the other hand, could contact their ISP, or even perhaps do things like a DOS attack or hack into it, putting up some not very nice things. (Not that I am advising that, of course. It is, nevertheless, an option, and should be taken only as such.)