The reason your social media reach and traffic have stagnated is likely due to a combination of factors. First, the overall organic reach of social media posts has been on the decline for several years now. Facebook's algorithm changes favor content that engages users and keeps them on the platform, which generally means shorter, lighter posts over longer, more in-depth articles or videos.
This shift has had a major impact on traffic to publishers' sites from Facebook, as noted by a report from Parse.ly. In 2015, the average referral rate from Facebook to publisher sites was down 20 percent compared to 2014 levels. The report also found that social media Referral traffic from Twitter was down nearly 30 percent over the same period.