In any social media campaign, you would have to set your targets. For example, if you're selling something, you could either set a target for number of purchase made from social media or the price value (ex. $1,000 for the duration of the campaign). In my past job, our target was X number of followers as we were trying to grow our social media following. If it's a video, you can set number of views and shares. If it's a contest or raffle, you could set the number of people who joined. If it's a live stream, you could set a target for number of viewers. It really depends on your goals on how could measure them.