I know what you mean when you say the player-base is low and hence, new players won't join and stay.
The truth of the matter is... if you're not investing at least $1k in advertising to penetrate the server-list saturation, then you're going to struggle.
The best thing you can do right now is develop a unique idea... display it in a well-developed package... and get a team of beta testers.
Offer giveaways, incentives and perks to new players. Promise them lifetime ranks for being first citizens. Find other servers that are struggling and offer to team up. Never bungee-cord your server with another, because then players will end up playing on one only, and you could lose players to a better server.
It's tough, but try not to spam or get players in a sneaky way. It's all about a unique idea to set yourself apart.
