test-connect blocks of machines?

Since NetSend is gone in Windows 7 we (like many others) still need to send broadcast messages to our environment.   I found the code below which works.   It allows me to send a MSG.EXE message to machines.   But the issue is I need to run test-connect first since I only want to send this Function to online machines.   

I know there are smart people on this forum and what I need help with is this:   if I want to send a House-Wide message I would of course get a list of machines from AD.    The variable below called$mypc would run Get-ADComputer etc...etc...  so now lets assume $pc has 2,000 workstation names within it.

How do I run test-connect against $pc but not one-at-a-time?  I want to ping blocks of machines and if they are online how would I then call this function below?

My goal is to send a message to every online Windows 7 machines within 90 seconds.   

Function Send-NetMessage {

Param(
    [Parameter(Mandatory=$True)]
    [String]$Message,
    
    [String]$Session="*",
    
    [Parameter(ValueFromPipeline=$True,ValueFromPipelineByPropertyName=$True)]
    [Alias("Name")]
    [String[]]$Computername=$env:computername,
    
    [Int]$Seconds="5",
    [Switch]$VerboseMsg,
    [Switch]$Wait
    )
    
Begin
    {
    Write-Verbose "Sending the following message to computers with a $Seconds second delay: $Message"
    }
    
Process
    {
    ForEach ($Computer in $ComputerName)
        {
        Write-Verbose "Processing $Computer"
        $cmd = "msg.exe $Session /Time:$($Seconds)"
        if ($Computername){$cmd += " /SERVER:$($Computer)"}
        if ($VerboseMsg){$cmd += " /V"}
        if ($Wait){$cmd += " /W"}
        $cmd += " $($Message)"

        Invoke-Expression $cmd
        }
    }
End
    {
    Write-Verbose "Message sent."
    }
}


$msg1 = Read-Host "enter a message"
$mypc = @("mg2014","cclab2","MG11751","mg10462","mg11768","mg11786","mg11741","mg13244","mg13434","mg14464", "mg10257")
$mypc | Send-NetMessage $msg1 -Seconds 30 -VerboseMsg

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mqh7