Hi. I have worked with a lot of eCommerce startups in helping them with their marketing. Based on my experience, the best approach is to start building out your mailing list. You can do this by running Facebook ads to a landing page and getting signups or running a social media contest. You should then set up an auto responder series in Mailchimp or any email marketing platform that you use to work your prospect into buying from your website. You should also set up retargeting ads using AdRoll or a custom audience pixel in Facebook to show display ads to your existing web traffic to drive them back to your website for a purchase.