Dear …
Once again we have managed to bring our __(name of event)__ to a successful close. It is our pleasure to announce that we were able to successfully __(describe what was accomplished in this event)__. Congratulations to all who contributed!
This event requires a tremendous amount of hard work to put together and we are so grateful to people like you, who selflessly volunteered your time to help us. Without your efforts, we simply would be unable to bring this event to life. To each and every one of you who so generously gave of your time, we extend our deepest thanks.
Thank you again, __(Name)__, for contributing your time to this event. We truly appreciate your support.
Sincerely,