Create the default groups via PowerShell
If your site is missing the three default groups “Visitors”, “Members” and “Owners”, you can create them easily with PowerShell or the Object Model.
Add-PSSnapin Microsoft.SharePoint.PowerShell
$web = Get-SPWeb https://your.site.url
if ($web.AssociatedVisitorGroup -eq $null) {
Write-Host 'The Visitor Group does not exist. It will be created...' -ForegroundColor DarkYellow
$currentLogin = $web.CurrentUser.LoginName
if ($web.CurrentUser.IsSiteAdmin -eq $false){
Write-Host ('The user '+$currentLogin+' needs to be a SiteCollection administrator, to create the default groups.') -ForegroundColor Red
return
}
$web.