Example scenario: a youth hostel employs someone to try get guests to be social and interacting. In a common area (lounge), the person may bring together various solo guests into a group and get everyone playing board games.
The end result being a better experience for the guests. The guests then being more likely to leave a positive review.
I experienced this some years ago at a hostel in New York. The social man later said he worked for the hostel to start such social activity. Long after, I saw a volunteer advertisement for the same thing somewhere else. I'm sure in that advert they had a word for the person who starts such social activity - I just can't remember the word.
Edit: Perhaps another take on this is someone who is planted within a group of people with the goal of influencing the group toward a desired outcome.