Why would you need a plugin for that... just go into the CP and create users.. Kinda ..... uhmmmm... won't say it... but it's not something I would do. Mine has been up for several months and I have a few users. Don't feel the need to inflate the user base. It will either take off or it won't - either way the domain is paid for 4 more years and the hosting is paid up for 11.5 more months.