Ohad Munder-Zichri's ninth birthday is on Monday, October 23.

But instead of celebrating at home with his family and friends, he is believed to be somewhere in Gaza, one of more than 200 hostages held by Hamas since the militants' devastating October 7, 2023, incursion.

The fourth-grader from the central Israeli city of Kfar Saba was nabbed along with his mother and grandparents during a holiday visit to his grandparents' kibbutz of Nir Oz along the border with Gaza.

Ohad's beloved uncle was killed in the attack. The boy, his mom, and his grandparents disappeared with the only thread of information about them coming from a cellphone signal traced to Gaza.

It's that uncertainty that has been most agonizing for Ohad's grief-stricken father, Avi Zichri.

"I keep imagining what he is going through. He's a sensitive boy. Did he see dead bodies? He wears glasses. Did they take them from him? Can he see anything?" Zichri said as he nervously chain-smoked cigarettes on his front porch.

"I keep thinking of every scenario, hoping for the least catastrophic. I just hope that he is safe and with his mother."

Zichri has been living this nightmare for 17 days, saying the thoughts never leave him and the only reprieve comes when he takes sleeping pills that knock him out for the night.

"And then I wake up in the morning and feel guilty for not thinking about them in my sleep," the 69-year-old said.

Ohad is Zichri's only child with his partner, Keren Munder, a 54-year-old special education teacher and volleyball coach for children with disabilities. He's also the only grandson of Avraham and Ruti Munder, both 78, who disappeared with them from Nir Oz, where about 80 people — nearly a quarter of all residents of the small community — are believed to have been taken hostage. Ohad loved visiting his grandparents and his uncle there.

At home, he is a gifted student who loves solving Rubik's cubes and playing soccer, tennis, and chess. He is a huge fan of Liverpool FC and his bedroom, untouched since his abduction, includes team souvenirs, his various trophies, family photos on the walls, and the elaborate Lego constructions he loved to build.

"He's incredibly smart and charming and is very developed verbally. He teaches me things all the time and I sometimes forget that he is only 9 years old," Zichri said.

Monday's birthday offered a chance to raise awareness of Ohad's plight.

There has been an outpouring of local and international support. The Israeli ambassador to the United States, Michael Herzog, launched an international social media campaign, calling on people to send him virtual birthday cards.

Members of Ohad's favorite Israeli soccer team and other prominent Israeli athletes have recorded birthday greetings and wishes for his safe return. Yellow balloons with messages recognizing his birthday in captivity were strewn across his hometown of Kfar Saba, with other local initiatives taking place. Local media widely acknowledged the day and friends posted tributes on social media.

Ohad's family members spoke with CNN about the 9-year-old and were asked what they'd say to those who apparently have him captive.

"Let them go," Itay Raviv said. "They are innocent. They are innocent civilians."

The family especially called for the release of the children. At least 20 of the hostages are believed to be children and teens, according to the Israel Defense Forces' estimates last week.

"We ask all media for everyone in Israel to hang a balloon," Merav Raviv, the niece of Avraham and Ruti Munder, told CNN's Jake Tapper.

For Zichri, Ohad's father, it was just another in a series of agonizing days, with anxiety consuming his every moment.

"I wish I could celebrate with him today. But it feels no different. It's just wake up and worry," he said. "And every day it gets worse."

Zichri was awaiting Ohad and his mom's return on October 7 when he heard air-raid sirens warning of incoming rockets. He instinctively reached out to Munder knowing that she and Ohad were in much closer range.

Pulling out his cellphone, Zichri showed their final exchanges.

"There is nonstop firing here and there is concern terrorists have infiltrated the villages," Munder wrote at 7:24 a.m.

She wrote that they were hiding in the safe room and she had locked the door. She said she forgot her cellphone charger in the kitchen and might soon run out of battery, but she managed to let Zichri know they had turned off the news so that Ohad could quietly watch a TV show to distract him from what was going on outside.

"Let's hope this ends quickly with no one getting harmed," she wrote in her last message at 7:39 a.m. "Take care of yourself and follow the homefront command instructions."

Zichri said it was typical of Munder to "always worry about others before herself."

Zichri said he shudders at every report of Israeli airstrikes in Gaza, wondering if they had harmed his loved ones. The only thing that keeps him going throughout the endless, agonizing wait for information is the support of a small group of friends and a vision of one day reuniting with his son and Munder, and falling into their arms in a tearful embrace.

"All I can do is hope," he said. "There is nothing else I can do."