How is social marketing different from conventional marketing?

Well, Social marketing is still the same as conventional marketing when it comes to the end result - highlighting the benefits of a brand/product/service to in order to raise awareness about it which in turn boosts sales and profits.

Also, the old and new 4Ps of marketing still apply to social marketing.

The difference lies in the "how" part. Social media marketing must be subtle and friendly without overselling. It's based on building one-to-one relationships and it takes some time to cultivate mutual trust but once the "right" relationships with influencers and potential customers, social media can be very rewarding.

Also, social media has been extensively used for market research purposes.