When this happens, most group leaders simply submit a general request to the group for help. I can't do it all myself anymore. I need help. The group has been watching, seeing how much you do, and they've noticed that it's worn you out. Instead, compose a list of tasks that someone else can take on for you.
People are much more likely to offer to help with a specific, clearly defined task.
Another effective option is to approach an individual for a specific job that they would do well. Mary, I understand you enjoy working on your computer. I'd be really appreciative if you'd help out with the newsletter for a while. I'm available to help you get started. Don't be afraid to call someone on the phone to ask for help.