An Israeli who crossed into Gaza last September is probably being held by the militant Hamas movement, Israel says.
Abraham Mengistu, of Ethiopian origin, went into Gaza of his own accord and has been missing since then, defence officials say.
Israel says it does not consider Mr Mengistu to be captive, AP news agency reported. Hamas has not commented.
An Israeli soldier, Gilad Shalit, was kidnapped and held by Hamas for over five years before being freed in 2011.
Israeli defence officials say they have appealed to international and regional bodies to help clarify Mr Megistu’s situation and are demanding his immediate release.
AP quoted an unnamed official as saying it is unclear why the 29-year-old went into Gaza but that he is believed to be mentally unstable.
Sgt Shalit was captured in a cross-border raid by Hamas in 2006, triggering a crisis which was only resolved years later in a controversial exchange for more than 1,000 Palestinian prisoners held by Israel.