Another clue to why someone is missing could be amnesia. How often does amnesia occur and how long does it last? Some information can be found in the link below. Feel free to discuss amnesia as a reason for a person going missing.
Gabriel Nagy, Severe Amnesiac, Reunites With Family After 23 Years
Most cases last for weeks or months, rather than years -- when UCLA honors student Ahmad Yaseen Arain vanished on his way to campus in 2004, he re-appeared six weeks later across the border in Tijuana with amnesia.
http://www.huffingtonpost.com/2012/08/07/gabriel-nagy-severe-amnes_n_1747869.html?1344360584
Gabriel Nagy, Severe Amnesiac, Reunites With Family After 23 Years
Most cases last for weeks or months, rather than years -- when UCLA honors student Ahmad Yaseen Arain vanished on his way to campus in 2004, he re-appeared six weeks later across the border in Tijuana with amnesia.
http://www.huffingtonpost.com/2012/08/07/gabriel-nagy-severe-amnes_n_1747869.html?1344360584