noun which may take the genitive case particle 'no', noun
missing; unaccounted for; whereabouts unknown
Primarily used for people whose location is unknown, often in serious contexts such as disasters, accidents, or disappearances. Can also be used for objects in formal or official language.
地震の後、多くの人が行方不明になっている。
After the earthquake, many people are missing.
彼の行方不明の財布がようやく見つかった。
His missing wallet was finally found.