VSTS Specified TypeScript compiler not found

Right click on Project and click properties Click on TypeScriptBuild and Select Use Latest Available

That means the TypeScript SDK has been updated on build server. If you are using private build agent, you can check it on your build server. If you are using Hosted agent, it will be updated irregularly (official article isn’t updated)

Regarding this issue, you can refer to these threads:

For VS 2015 project (Microsoft.TypeScript.MSBuild package): Visual Studio Team Services build Typescript error

For VS 2017 project (Microsoft.TypeScript.MSBuild package): Angular4.1 with .NET Core1.1 build fails in VSTS Hosted VS2017 agent