When it comes to choosing between social media and digital marketing, many companies have their own set of arguments. It often depends on the service provided, brand or product. In certain situations, digital marketing may be more appropriate to build awareness than social media. The latter is often advised when the audience is broad and spread at a larger scale (national, international).
For example, if your company sells software solutions, it might be best to use social media to find customers, explain to existing customers how to use it, and keep them as informed as possible with updates via press releases, email subscriptions, tweets and shares.
But if your business sells custom tools for constructors, social media is not that useful because it can only be employed to find information on the products. You need people buying what you have to sell, and to convince them you need to give them a taste of the product first hand.