There are several possibilities for magical groups. While players are encouraged to join other groups made up of Missions players, to build community ties, it is not mandatory to do so.
LINK A Combat focused group for Adepts.
LINK A Stealth focused group for Adepts.
LINK A Zoroastrian group
LINK A collection of groups.
If you have affiliations with certain corporations, membership to an initiatory group may be available for successful completion of a project. The Illuminates of the New Dawn are always accepting new citizen-candidates for the SINners amongst you, and the Rat Pack may be available to certain runners who have made the Neo-A's watch-list of talent.
I hope that helps give you a feeling for some of the groups and flavors out there at the moment. If you want to start a group and don't know how, Aaron or I can help walk you through the process. You can also post here, the DemoTeam player's registry, or on other forums if you are looking for other Missions players from conventions or local events to team up with and initiate.
If you have other questions, you can also check the Missions FAQ
LINK. (I point this out last since the Magic Groups question wasn't in there explicitly.)