Few things are as powerful as a personal invitation. A personal invitation says “I want YOU here” – not everybody but you in particular. It says “I find you valuable.”
If you want someone to show up, and if it is at all possible, send a personal invitation. Not a form letter or newsletter made up to seem personal. Not a Facebook event or Meetup with them on the guest list.
Send a handwritten note, pull the person to the side, or start a direct chat with them. Despite our modern technological age, the personal touch is still the real magic.