First of all figure out what your goals for each platform are. Next the whole point of being active on these platforms is engagement. Start measuring how many people are engaging with your content i.e each post, tweet, pin etc (experiment with the content). Then figure out how many clicks you are getting from each one. Followers, fans are also good metrics to make sure you're growing (don't buy them). Also try running ads on each platform and calculate out if they are worth the cost as compared to your lifetime value of a customer and the average customer acquisition costs.

Great advise...I never thought of runnings ads as an experiment.

No problem. Definitely can run ads for things like getting fans for facebook pages. Just start with a small budget and see if anything comes out of it.

Start with what does "winning" look like and then work backwards from there until you feel you have enough visibility.

What you measure will be completely up to your strategy.

Thanks for your advise. Makes sense. One of the problems was to figure out what "winning" looks like. We have a sense of what we need to achieve and are driving towards that goal. But would like to make sure are not missing anything.