Is it the biggest bitcoin poker site out there? I saw about 180 online users and its quiet low amount.
I think you should do a small refferal bonus to make people advertise.
They already have an affiliate program:
https://swcpoker.eu/affiliates/It's actually pretty generous if you have a good network of contacts to refer.
The old sealswithclubs often had between 300-500 players online in the final months, which is a respectable figure in my opinion. It was enough that you could find action at basically any stakes at almost any time. That's not something that I've found elsewhere, but then again, a lot of the other provides ask you for dox or they don't run on linux or some other stumbling-block. Nowadays swc is without it's non-windows people. I think once they straighten that out they'll see their numbers basically double from what you're seeing now.
I agree about the number of players, and you know what, 300+ can be enough.
About the affiliates, I actually dont have any specific plan of advertising as they write in the page, but I believe that I can bring at least 10 players in my ways with small investment of time and money. And i believe there are more like me.