If you want to find interactively logged on users, I found a great tip here :https://p0w3rsh3ll.wordpress.com/2012/02/03/get-logged-on-users/ (Win32_ComputerSystem did not help me)
$explorerprocesses = @(Get-WmiObject -Query "Select * FROM Win32_Process WHERE Name='explorer.exe'" -ErrorAction SilentlyContinue)
If ($explorerprocesses.Count -eq 0)
{
"No explorer process found / Nobody interactively logged on"
}
Else
{
ForEach ($i in $explorerprocesses)
{
$Username = $i.GetOwner().User
$Domain = $i.GetOwner().Domain
Write-Host "$Domain\$Username logged on since: $($i.ConvertToDateTime($i.CreationDate))"
}
}