I suggest that you find forums related to your topic, review them, join the ones that suit your topic best and add good useful comments/posts on there. Create a signature with a link in it back to your site. You will need to understand the forum’s rules about posting and signature links so you don’t break their rules and get banned.
Also find relevant Facebook groups and do the same. Again observe their rules else you will get your account closed down. Reddit is another good source of free traffic using the same principle but in all cases you must obey the rules and not spam dozens of posts and comments a day just geared to get links back to your site.
All free traffic methods are going to be slow so you must be prepared for that. That’s the benefit of paid traffic, it’s almost immediate and you can have more control over it.
However, the people who can help you best don’t have the best reputations. It’s because they are similar to publicists. Ultimately, the skill-set for running a business through social media is being an author/entrepreneur.
If you look at what you are building from an author’s point of view, you have built an audience through writing. It makes sense to begin writing your book. You can include your audience in the writing of your book by make facebook pages or even a whole website with all types of goodies for your audience to peruse and comment on, surveys, videos, stories of your processes.
There are lots of people out there offering courses, webinars, and all types of online programs in building a social media empire. What’s surprising is how much free information there is. Since you have 12k likes you have the chance to build a large list fast. If you have $1000 to invest in a class, by all means do it. If you don’t have the cash. Just sign up for free content. You are looking for the best ways to market to your established audience and there is a ton of free content given away on how to do just that. What you pay for in a paid class is the feedback and confirmation by the teacher as well as contacts with other students. I can tell you which teachers I would recommend by PM or if you reply to this post. BUT, no way will I volunteer these guys names. They get the brunt of negative feedback because they have 5% and 7% success rates with their students. This is actually much higher that my Fine Arts program in college that had like 1 % job placement rate over the first 15 years after graduation. I think it plummeted after that I think it’s higher than the writer’s society I belonged to. It probably had a .5% success rate in getting members published and listed.
So, are you ready to step into the spotlight? Be ready to get aimed at by critics and naysayers. But also, be ready to connect with your audience in new and valuable ways. If you have that many likes, you may have the beginnings of something big. Give it a chance and make wise decisions.