As far as I can tell, JetBrains' support for Microsoft Team Foundation Server or Visual Studio Online/Visual Studio Team Services is limited to a plugin that allows IntelliJ to access Git repos through TFS. There is a 3rd Party plugin for IntelliJ connectivity to TFS, but it doesn't appear to authenticate properly against VSTS (I need to spend a little more time messing around with it, but I haven't been able to connect yet.).
It would be awesome to see an official JetBrains plugin for VSTS that allows Rider/IntelliJ to access VSTS repositories, and not just Git. It would also be great if that plugin could use VSTS access tokens for authentication in addition to username/password logins, but I'd take VSTS/TFS repo access over tokens any day.