Map out the pathway you want your target audience to take as a result of your storytelling. Monitor to see if you attained the desired actions at each step of your conversion path, whether it's a purchase, a visit, a click or a commitment of some kind.
Measure how effective your content is at building a loyal audience that is open to hearing more from you. Report on follower and email list growth. Or, if you are marketing an event, report how many attendees responded and then attended.
Powerful storytelling is shared, earning greater reach. Measure virality through social shares and email forwards separately from other engagement measurements--they matter more!
How long were your videos viewed? ThruPlay or 2-second consecutive view? Measure storytelling effectiveness by the length of time people spend watching your video.
Use Google Analytics to measure engagement with content on your website, such as articles, videos, calculators and other tools. The metrics to use are Time on Page, Pages Per Session, and Session Duration.
Look at bounce rate trends for your whole site over time. Some content such as blog posts can have a high bounce rate, which isn't necessarily bad, especially if the metrics above look good. You can remarket to those site visitors.
Individual post reactions are directionally helpful, but the metric you want to monitor is how social actions change over time and if those trends correlate positively with other business KPIs.