Most people don't realize that Riki can pull of a great support. Here are just a few scenarios in which you would play Riki support:

-Riki is picked/randomed early, and the other team counters
-Many supports require initation/escape/roaming in order to set up ganks, Riki has all of this built in with Blink Strike (blink dagger) and Invisibility (Shadow Blade) without needed to spend money on those items.
-It's unexpected, and generally people will either try to target you (and you can escape and let your team clean up while they chase) or they don't target you (you keep them disabled).