Social media is a double edged sword. On one hand it gives wider exposure, but a lot of it may be trash and eats up a lot of time of employees affecting their productivity negatively on the other. It needs to be used with great caution to develop effective and meaningful networks.
social media has emerged as one of the powerful tool creating opportunities for organizations to promote collaboration between employees and to improve employee engagement. the following research link may be more useful for developing the construct for the study.
In this survey social media is positively related to affective commitment, but in many study has no strong relationship between commitment in workplace and using of social media.
A Social Media could impact and influence on employee engagement by applying Psychological Roles including: Attitude, Perception, Personality and even relevant Culture, and Learning. The most suitable reference in this reason for guidance of your study is the book titled "Organizational Behavior" by Stephen Robbins.