I’ve had most success by placing an ad in AR on the forum and regularly updating it. Active players are also making their own posts in alliance recruitment, so I would encourage responding to these ads - yes there will be a lot of competition from other recruiters too, so being clear about what differentiates your alliance from others is important.
As @JonahTheBard has mentioned there are also recruitment chat rooms on both the Line app and Discord. AR on global chat is not for the faint hearted but I’ve had success there too.
Good luck