Without buying ads, FB can still send thousands of daily visitors to your site. Most are just curious, but many can become valuable repeat traffic.
• Create images about 600pxl x 600pxl that represent some of your web pages or articles.
• Install Og code
[ogp.me] in the HEAD section of your HTML markup using that image and write title and description.
• Join topic related FB Groups. Join a lot of them. Participate. Make friends. Comment on posts. Like posts by others.
• After you've established yourself as an active member and not just a spammer, start to post in each of these groups, a couple times a week at first. Later you can post more often. Be careful not to post too fast. Wait at least 60 seconds between posts or the FB anti-bot system will catch you and suspend your posting rights.
The Og images will automatically link to the target page and supply a title and description that you've included in the code. These posts look nice and the better the image, the more traffic they will generate, but the target page will need to give the visitor something of interest or the group will quickly label you as a spammer, so write good content at your site :)
Sometimes it may be necessary to load the Og image into FB's cache system. Use this tool. Run it a couple times: [developers.facebook.com
The Og images/code also works for Twitter, Google Plus and a few other SM sites.
Here's a similar tool to get Twitter to load the OG image: [cards-dev.twitter.com