The simple answer to getting your customers engaged in social media would be to ask them. Does your ecommerce shopping cart integrate with any type of commercial or open source customer relationship manager? Add their social network information and build your followers.
Next, submit your onsite content to social networks. Understand the purpose behind each social platform. You may broadcast timely promotions via twitter or you may produce consumer education content via google plus business branding or google local business branding. If your target market are to other B2B clients, post to linkedin.com
Follow up in a timely manner to show your clients and potential market that you listen and you care. Avoid sending mindless canned responses. Customize your message on each engagement.