I recently found myself in a situation where I needed to publish my artifacts to the team city’s internal nuget feed server DURING the build (not after). In order to accomplish this I had to let Team City know about my artifacts folder (or files) during the build. I simply needed to output a message. I used Team City’s Service message syntax to do this. In my build project I create another target step:

<Target Name="ExposeArtifacts" DependsOnTargets="CreateNugetPackage" AfterTargets="CreateNugetPackage">
  <Message Text="##teamcity[publishArtifacts '$(Root)\_build\Artifacts']" />