I just launched a non-english website, for selling and buying used phones. I have been reading a lot about SEO but most articles are targeted towards blogs. I wonder if anyone could give me some ideas on how to get any backlinks and how to rank for specific keywords.

• 90% of the content on the site is generated by users, so I can not really put keywords there myself.
• However, the adverts posted by the users usually also contain keywords such as: iPhone 7 For Sale, etc..
• I can not really do guest blogging either to get some backlinks, because this is not a blog.
• The site has a pretty stable following base on social media, but I heard those links don’t really make a difference
• Despite these, I have keywords in the title tags, img tags, descriptions and etc.

I am also struggling to get people to put there ads on here, obviously because they don’t necessarily trust the site yet. Any ideas on how to advertise such site? Do Facebook ads actually work? Is AdWords any good here?

How did Craigslist, eBay for example gain initial traction?