Try joining Spooooky Ghost Tour Planning Association Group, they are great. I found my last ghost on one of Arya's Ghost Tours, it was lots of fun. If the tour is not for you, there is a list of all the known ghost locations in the wiki:
http://www.glitch-strategy.com/wiki/Notice_the_Unnoticeable
Are there usually more than one in an area for each player? I'm going through the locations, but it would help if I knew I could move on once I find one.