How would you market a web directory?

Ok

So I have this site for personal trainers. They can join, promote themselves, links to social media, direct contact form, phonenr, pictures and about them. I charge a small fee.

Before the site was up I created a facebook page, instagram profile and twitter-account
They reached 80, 2000 and 90 people, most of them personal trainers . (I live in a small country with 5 million people, but huge demand for personal trainers - rich western country)

I asked them if they wanted to join for free for a year (test pilots) and I collected a what I thunk decent crowd (70 people)

I reached them mainly by instagram I think, but also Facebook by posting in public groups, also did alot of emailing. I had a list of about 2000 people, and 80 wanted to join right off, so 4%.

Now..I have to do TWO things. I need more trainers to pay to be on my site..but why would they wanna be there if no one is using the site, or know about the site. Right? So I need to market the site to users of the site - people who are looking for PTs.

This is where Im starting to become crosseyed...

I understand I will have to do adwords, facebook, instagram and probably email and calling to get to the PTs(no one really use twitter anymore) But lets say Facebook..man Im really struggeling to get likes. 100% of likes are PTs..so theres no point of marketing anything to the customer on my page (because why would i market "try John - hes a great PT" on a page where 100% are PTs themselves.

So I should probably do facebook ads traffic for website?
Trying to pay for likes only get me asian women who claim they live in my country, but they obviously arent.
Should I focus a lot on Instagram? It seems pretty easy to build an audience (took me two months to get 2000 followers, but I also spent about 2 hours every day on it)

Ah this is getting too long..Any advice so far? Other than the obvious ones? Where should I focus my thinking?