Pluto is not, and never was, the 'ninth planet' that was being looked for prior to 1930. When it was found, it was mistaken for that planet, but it was soon realized not to be anything like they were looking for. It was called a planet because they didn't know what else to do with it, having not yet discovered any other bodies in its class.

The search for the 'ninth planet' continues, regardless of Pluto, whose existence is irrelevant to the question at hand. For a while they were calling it the search for the tenth planet.