Paul Jarzembowski provides church document resources, which will help to build a firm foundation on building a strong young adult ministry.
Consult the Church’s documents on evangelization, formation, and young adults, specifically Go and Make Disciples, Were Not Our Hearts Burning and Sons & Daughters of the Light (see a summary outline here). These will give you a firm foundation on our mandate to reach out, teach, and build relationships with young adults today.
Check out other steps in starting a young adult initiative in the Essentials section.