Board Thread:Support Requests - Getting Started/@comment-27162338-20160519004946/@comment-5650583-20160519012843

You cannot make a private wiki on Wikia. The best thing to do in this case is to keep an eye on your wiki and revert spam/vandalism when it happens. Once you have established a community, you can begin to promote trustworthy users.

While you can require users to log in before they edit, I think that may require Staff approval.