Over 20 million people are active on Facebook, Twitter or Instagram at any one minute so why not go where the people are? People are more likely to react to a great advertisement on their phone than taking the time to read the newspaper or search for those yellow pages.
A second thought is with social media you can quickly engage with your current and potential customers by posting specials and asking for customer feedback. The last I checked, it is pretty tough to acknowledge customer feedback in the newspaper.
The problem with most businesses is that they do not have the time to engage with customers and actively post content on the social media platforms and they are right. Business owners normally need to focus on their business whether it is service oriented, their art (music) or a trade. Spending money on a Yellowpages ad or newspaper advertisement is easy and fast and they assume they work. Most businesses do not have the time to measure the Return on Investment from their ads whether they are offline or online.
In reality, a simple social media post has more reach than a newspaper advertisement or a TV Commercial, since a post can go viral with the right keywords and get re-posted over and over again for free. Try placing a second newspaper ad for free.
So in closing, before taking a leap into the world of online marketing, take a look at your business goals. Are you meeting your revenue projections? Do you have enough customers? Are you getting the right customers? Have a solid business plan and a way to measure what type of marketing can be successful to grow your business and then engage a digital marketing expert to help you. Digital Marketing is a full time job and you will need to focus on your expertise/trade first.