While they're found on all such sites, they seem to be most accessible on Twitter. (They love Linkedin as well, but they're on there more to connect with peers and potential employers rather than the general population.) So anyone with a website should make a point of using Twitter to seek out journos in their niche -- preferably ones from their own country -- and build rapport with them.
Journalists are always on the lookout for knowledgeable and interesting people who can supply them with compelling content. And if you've gotten on their radar by tweeting and impressed them with your expertise, there's a good chance they'll ask to interview you at some stage. If you can get them to mention your website when they do so it will help you enormously, even if you don't get a backlink from it.
Speaking of backlinks: Remember also that many journos maintain blogs hosted on their employers' sites. Getting a backlink from a highly ranked, frequently indexed website like News Ltd. or Fairfax is very powerful. It's like getting a .edu link.
So keep an eye out for these blogging journos. Engage with them on Twitter and comment thoughtfully on their blogs. From time to time you can send them links to your own blog posts that they might find interesting. Sometimes they'll like your blog post enough to quote it, along with a link. But even if you haven't blogged about something yourself and merely point them to something interesting, they will often include a "hat-tip" link to you as a mark of appreciation.
I know this works from several years experience of writing political blogs. Over that time I have received many links back to various blog posts from big name bloggers such as Andrew Bolt and Tim Blair. They've helped enormously with traffic and SEO. (While both of these particular blogging journos aren't actually on Twitter, plenty more are. And it's clearly the easiest way to connect with them.)