Honestly, I'd stick to SEO and social media promotion. Buying traffic can get costly, and regardless of what anyone tells you, there are no guarantees with it. You can rank for a keyword, and you know you're gonna get traffic. But if you buy visitors, then there's a chance they're not even going to be interested in your sites.
Think about it for a second.
If someone clicks your website from the search engine, it's because they were looking for it. But if someone happens to see your site by whatever traffic delivery system, there's a chance they won't even care what your site is about.