How should we evaluate Social Media Influencers?

Taylor Lorenz writes an interesting article about how hotels are struggling to identify the right social media influencers to better market their properties. My biggest surprise from reading the article is that it does not appear that hotels have a systematic approach to evaluating influencers. It seems like they have taken more of a spray and pray approach. 

As a blogger trying to grow my audience, I've become interested in finding the best places to share my content. Thus far, I have shared posts on Facebook, LinkedIn, KevinMD, Instagram and Twitter.  In my limited experience, my Facebook network brings the most eyes to my blog, despite reaching a much smaller audience than other avenues such as KevinMD which gets approximately 3 million page views per month. I suspect the outsized response is due to the fact that my Facebook Friends feel more connected to me and are more willing to engage with my content.  Other than through trial by error, I'm not sure how to assess the level of engagement with users on other platforms. It is nice to see that I am not the only one struggling with this issue.

Please use the comments sections to share your thoughts regarding how you've evaluated/identified opportunities to grow your audience.