Nothing has been heard of Sgt Shalit since June last year
Hundreds of Israelis have gathered in Jerusalem to call for the government to step up efforts to free Gilad Shalit, a soldier captured by militants in 2006.
The protesters joined Sgt Shalit's parents, who are staying in a tent near the house of outgoing PM Ehud Olmert.
They want their son freed as part of a prisoner swap with the Palestinians.
At one stage, crowds of protestors blocked the road leading to Olmert's residence, chanting: "Olmert, you made a promise, Olmert, keep it."
The Shalits say they fear a more harder-line cabinet led by Prime Minister-designate Benjamin Netanyahu might be less likely to do a deal.
Sgt Shalit's father, Noam, told Israeli media he was encouraged by the show of support.
"We only organised the place, not the people. They came from all over the country spontaneously," he told the website of the Yediot Aharonot newspaper.
Sgt Shilat's case is a highly emotive issue in Israel
The Shalits set up a tent in front of Mr Olmert's house in the early hours of Sunday, escalating their campaign after the prime minister said demonstrations calling for Sgt Shalit's release were unhelpful.
Mr Olmert had made the release of Sgt Shalit a major issue of his premiership - but has only weeks left in office.
Gilad Shalit was seized in June 2006 by Palestinian militants, including members of the Hamas group which runs Gaza, in a raid into Israel that also left two Israeli soldiers dead.
Egypt has been brokering talks to secure his release. Hamas are demanding the release of more than 400 of the thousands of Palestinian prisoners held by Israel.
Nothing has been heard from the Israeli conscript since June 2008, when a letter in his handwriting was delivered to the Carter Centre in Ramallah in the West Bank.