First and for most you need to build the foundation of your site. And when everything is ready, you can promote your site using different social media accounts. Like for example, you can create Facebook page get your friends to like it. By then you can share or promote your link on your Facebook page where your friends can see it and they can share it. You can use Instagram account, if you don't have an account, you can create pretty easy by linking your Facebook account. And from there you can follow everyone and they will follow back. You can promote your link from then. You can also promote your ecommerce site using Youtube channel by creating sensible video and include your link on the description. Try to be engage with your audience once they start a conversation so you can keep up with them.