It’s a good practice to skew your communications efforts toward newcomers or “outsiders”, inviting wider participation. Explain the event or group in a brief, easy-to-understand way, without assuming that “everyone” knows what that event/group is all about. And always, always, provide some way to connect. Telling readers how to connect is a call to action and an invitation to participation.
That can be as simple as: “To join the choir, simply show up at the Thursday, 7 pm rehearsal.” It can be an email address, as in: “To volunteer, email Suzy” (embed Suzy’s email address as a link to look more professional). Since you’re using digital media, the preference would be to let people respond by digital media (ie. an email or on social media like Facebook) instead of having them make a phone call, which requires a much higher social inertia to overcome (that is, it’s easier and preferable for most to email rather than call). While you are at it, make sure you are providing ways to connect when using other digital media like an email newsletter or social media.
Do you make an invitation to connect a part of your promotions? What’s been most effective for you?