I see the new Build definitions of Visual Studio Online have not supported 'Azure WebApp Deployment build step' to deploy Virtual Application (Sub site).
So I try on using 'Azure PowerShell build step' but couldn't find out the script.
I also tried this tutorial: https://msdn.microsoft.com/en-us/library/azure/dn642480.aspx?f=255&MSPPError=-2147217396
But stuck in step generate folder called PublishScripts. Because I've already created Azure WebApp and VSO Project, not starting at a blank.
Updated: I've solved by creating & upload a custom tfx build task based on ps msdeploy.exe
You should use the build in Azure Web Application deployment step.
This is by far the easyest method.
I've solved by creating & uploading a custom tfx build task based on ps msdeploy.exe