This is just an example that may be helpful to you. It also contains a helpful link for new members.
Example Welcome Message:
Welcome to VoteCitizens.Org, the official social network of the Citizens Party of the United States. We're happy to have you!
You can find lots of information on our Get Started page to help you learn your way around.
Let me know if you need anything.
Good guidance here. Gets one started on a more personal greeting, should that be desired. And I think it will.