Ghost hunters are either individuals or groups of people who have come together in an attempt to study and find evidence that ghosts exist. Ghost hunting is mostly a hobby for those who do it, though the motivations are usually a combination of three kinds:
Ghost Hunting for The Sport - involves hunting for ghosts simply to satisfy your own curiosity or for the thrill of it.
Ghost Hunting for Research - involves hunting for ghosts to provide physical proof of ghosts and hauntings.
Ghost Hunting to Help - involves hunting for ghosts in an attempt to help counsel the souls who are still lost and the people being afflicted by those souls so that each can move forward into a more loving experience.
Most ghost hunters do this for all three reasons, and I believe the most important part of ghost hunting should be the third one, to help any lost souls move forward, and also the families that may be negatively affected by those souls. Many ghost hunters organize themselves into local groups of paranormal investigation teams. A local group has most likely already formed in your area. If not, maybe you could be the one to start one! Although the gear and equipment for professional ghost hunting can get a little pricey, most ghost hunting groups provide their services to people and families free of charge.
If you don't already belong to a ghost hunting group, do some searching in your area to see what's around. Some groups are very large and well funded already, while others may just be a few friends who get together with their digital camera on weekends to see what they can find. Ghost hunters come from the occasional hobbyist to the full-time professional paranormal investigator and everything in-between.