Social Media Today reporting:
The commonly stated best practice for hashtags on Twitter has been two, with research showing that engagement drops significantly once any more than two hashtags are used, on average.
...The commonly stated best practice for hashtags on Twitter has been two, with research showing that engagement drops significantly once any more than two hashtags are used, on average.
...TrackMaven found that nine hashtags is the optimal amount for boosting engagement on the platform...
http://www.socialmediatoday.com/social-networks/new-report-looks-optimal-hashtag-use-twitter-instagram-and-facebook?utm_source=Sailthru&utm_medium=email&utm_campaign=Newsletter%20Weekly%20Roundup:%20Social%20Media%20Today%2010-22-2016&utm_term=Social%20Media%20Today%20Weekender