I've named a star and would love to be able to find it in the sky - is there an app I can use to locate stars given a specific coordinate?
There are apps which will help guide you to more significant stars (Google skymap comes to mind if you're looking for a simple mobile system - Stellarium may also be a good option), but it's highly unlikely that any app will include the location and names of so-called 'personal' stars, as the bodies who sell such things don't have any the authority to do so and are not generally recognized in the actual world of Astronomy.
Note that the IAU (International Astronomy Union) is the body generally recognized to have the responsibility of naming and classification of stars and other bodies. They also come out strongly against such practices and services:
As an international scientific organization, the IAU dissociates itself entirely from the commercial practice of "selling" fictitious star names or "real estate" on other planets or moons in the Solar System. Accordingly, the IAU maintains no list of the (several competing) enterprises in this business in individual countries of the world. Readers wanting to contact such enterprises despite the explanations given below should search commercial directories in their country of origin.
Alternatively, if you were to get the Right Ascension and Declination coordinates from the company that sold you the star you could use a database like SIMBAD to find the actual designation of the star you purchased. You could then probably use the SIMBAD designation to find the star using Stellarium.
Here's a link to the SIMBAD database: http://simbad.u-strasbg.fr/simbad/sim-fcoo
I hope this helps!