You're telling me he pays people to pass themselves off as him?
You're joking, right?
If not, yeah. The overwhelming majority of "celebrities" pay people to do this sort of work for them. They may have a team of people posting as them on Twitter, or on Facebook. They also pay people to sign autographs through the mail. If it surprises you to know William Shatner doesn't answer his own fanmail, then I'm sorry but the reality is they don't.
Mira Furlan, Pat Tallman, Claudia Christian, and Jason Carter have been off Babylon 5 for about 15 years. With the exception of Mira's role in Lost, none of them have had a "hit" since then. Yet all four have teams of people who post as them on Facebook.
George Takei has his own team of people who do the same thing.
What makes you think Shatner is the exception? That he's waiting by the computer, desperate, hoping someone is going to send him a message on Facebook?