This might sound a bit insensitive with the recent/local case, but missing persons cases are VERY fascinating...to me. Especially those where there's no logical answer.
I'd say the vast majority are Occam's Razor with fairly normal circumstances. i.e. domestic or drug related or human trafficking, etc. I'd put the Lincoln disappearance in a normal and/or domestic category on the little information provided.
But there are a reasonable number of missing people that have weird and unexplainable circumstances. They literally disappear from the face of the earth never to be seen again. Additionally there are instances where an area is searched repeatedly, and then suddenly the body appears in the area that was searched over, and over, and over. This oftentimes leaves local, state and even federal authorities dumbfounded with no logical answers. Typically in normal circumstances there will be evidence left behind such as tracks, DNA, personal items, video, etc.
Torture for those families that don't have any closure whatsoever.