Kuala Lumpur, Malaysia (AP) — Families of the 239 people on board Malaysia Airlines Flight 370 were marking the anniversary of the plane’s disappearance Sunday with a vow to never give up on the desperate search for wreckage and answers to the world’s biggest aviation mystery.

Voice 370, a support group for the kin of those on board, will host a “Day of Remembrance” at a mall in Kuala Lumpur. Later Sunday, the Malaysian government will release an interim investigation report, a requirement under international civil aviation regulations.

Although no wreckage has been found, officials in Australia, Malaysia and China, the three countries leading the search effort, say they are still optimistic the plane will be found in the southern Indian Ocean where they suspect it crashed after deviating from a flight to Beijing.

A year without a clue to the tragedy has frustrated the relatives. Grace Subathirai Nathan, whose mother Anne Daisy was on the plane, said today’s events were important “to highlight to the public that we still don’t have any answers and that we must pursue the search.”