Every diocese is encouraged to consider sponsoring diocesan Pentecost Vigil Celebrations. They can be hosted at any parish or at the cathedral. In the case of especially large dioceses, multiple regional events might be more advantageous than a single diocesan event.
If your diocese plans to sponsor a Pentecost Vigil Celebration and you are a young adult and would like to help, contact your diocese and ask to be referred to the organizers. They will be grateful for your assistance. For a list of dioceses in the United States, see http://www.usccb.org/about/bishops-and-dioceses/all-dioceses.cfm
If your diocese has not yet decided to sponsor a Pentecost Vigil Celebration, or if you are not sure, contact your diocese and the office responsible for young adult ministry. Let them know that you are interested in participating in a Pentecost event and would be available to help. If you are willing to take on a leadership role in organizing the event, or if you have friends who would also like to volunteer as well, let them know that as well. While every diocese is encouraged to sponsor its own Pentecost Vigil Celebration, local support and the availability of volunteers will undoubtedly play a crucial role in its decision.
If your diocese is not able to sponsor a diocesan event, an individual parish might be able to work with the diocese to produce jointly sponsored event. An individual parish can also simply sponsor its own event.