Content seeding

Hello, colleagues!
I have a question about the instrument which is called “content seeding”.

What do you do if you need to show some content (for example video) to a large number of special target audience? The simplest instrument seems like any landing with this video (facebook post, tab, website) + some kind of ads to this landing (facebook ads , media ads, search ads), but sometimes the view of the video will cost you much more in that way.

For example there are many communities on any topic in Russian social network VK. The largest communities in VK aren't branded. there are communities larger that million users where young people are posting memes, there are communities for moms and housewifes etc. So depending on the target audience, we can place the necessary branded content directly in the communities with needed audience, because most of these communities sell posts. So it’s like “Promoted posts” in Facebook which you can target very precise and show not only to friends of people who like your page.

The largest communities in Facebook are already branded. There aren't pages and groups by interests with millions of audience. Do you use «Content seeding», and what do you do to accomplish such task? Bloggers? Platforms outside social media? Is there a database of non-branded FB communities with big amounts of audience which is necessary to contact to work in such way?

Thank you a lot!