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 lowers 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! Also success is determined around the resources that you have, such as your organizations 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!