Whether or not social media is the best way to advertise depends on your offering, audience, and resources. Social media offers a way to advertise more directly and targeted than traditional media- which has dramatically lowered the cost to start marketing there.
However, success is determined by the audience that you have, as different audiences will have different mediums that they are on. Thus if you market on the wrong mediums, you will get less than desired outcomes!
Success is also determined by the resources you have, such as your organization's creative and storytelling abilities.
In summary: social media a direct and targeted marketing solution but is no silver bullet because it requires investments to mark it successful!