Thanks Dave,
You do need the double double quote, as I'm using it in PowerShell script
Guess I figured it out using Start-Process
In script:
$search = "Hello World"
$indexName= "myIndex"
$args = "-c ""\""$($search)\"""" -idxname $($idxName)"
Start-Process -FilePath 'C:\Program Files\Mythicsoft\FileLocator Pro\FileLocatorPro.exe' -ArgumentList $args