The official supporters' body for the WHR Project is The Welsh Highland Railway Society.
The Society coordinates most of the volunteer activity on the railway with the various company departments, eg trackwork, maintenance, train staff etc. There are other groups active and Team Wylfa is one in example, although their work is still carried out in conjunction with the society or railway company. Further details are to be found on the Society's website.
Many of the volunteer activities are listed and reported about elsewhere, however, the Volunteer Projects page gives on introduction to the activities and provides links to where to find more information. As well as this page there is also the Society's Volunteering page that gives a good introduction to the sort of activities available for anyone wishing to become involved.The Tale of a First-Time WHR Volunteer - Gives a good idea of what to expect on a working trip to the line.
The Welsh Highland Heritage Group looks after the historical aspects of the railway and membership details are on their website.