OK you can't precisely measure the total success but you can measure various components that make up the campaign success and by examining the overall change is these components you can know if your efforts are being successful, neutral or actually hurt your brand.
The first step in measuring success is to stop calling it social media. Social media are the individual tools used to spread your marketing message through social interaction (word of mouth marketing). For example placing a phone a call, holding a webinar, setting up a facebook page, establishing a Twitter account, creating social content (a blog), etc. When you add the different social media tools used in your campaign together you get a "social marekting campaign". Now that we got this settled, we can go about measuring the success of the campaign.
The primary purpose of any social marketing campaign ("social campaign") is to draw people together who have a common interest (your product). You can then engage and interact with them. For each organization you first need to identify and define your goals and objectives for this interaction. Typical ones include:
- brand awareness;
- increase in sales;
- improved customer relations;
- improved customer satisfaction
With your goals clearly defined and a methodology in place for measuring them, start your social marketing campaigns one at a time while holding all other marketing efforts steady. Now wait and start measuring. Social Marketing/Word of Mouth Marketing takes time. So give you campaigns time to rise and shine and don't expect an instant home run.
Just imagine a twitter campaign when you have zero followers. What can you expect? Nothing of course. It takes time and an ongoing effort to build up a loyal following. In the early stages of a twitter campaign your goals and measurements have to be around follower growth and engagement. Once you established a solid foundation, you can then start marketing to them as part of your overall engagement. Who you engage and market at the same time is a tricky manoeuvre and unique to your particular audience and how you built up trust.
This same measurement concept will also apply to Facebook, G+, blogging campaigns and any other form of word of mouth marketing. If you've developed a loyal following and customers and you given them something to talk about they will. And the more they talk (presumably positively about your brand) the more growth in followers, customers, sales and ultimately profit you should see. After all, isn't an increase in profit the ultimate ROI because without profit, our businesses will cease to exist.