I am currently trying to a build definition on VSTS. I am using Hosted agent, but for some reason it seems i am missing a lot of built in tasks. I am missing several of the task
It is already in VSO but not enabled for customers yet. Refer to this link for details: https://github.com/Microsoft/tfs-cli/issues/30
The IIS Web Application Deployment task still seems to be in preview. Meaning it is deployed to your tenant but not enabled. Therefore you also won't be able to just upload it yourself using Tfx-Cli.
The only way to have access to them seems to be if your tenant is in preview mode which you can request from the address mentioned under contact on this site. See also this issue.