Tel Aviv – Israelis were searching Sunday for loved ones who were taken hostage or went missing after Hamas’ brutal attack on the country the day before. At a makeshift center in Tel Aviv, dozens of people gathered to try to obtain any information they could and deposit DNA samples to aid in the research.

Families sat on benches inside a regular lobby or waited outside, where volunteers distributed snacks and drinks in the hot weather.

The sisters, Inbal Albini (55 years old) and Noam Berry (40 years old), were among those at the center, searching for any trace of their father, Haim Berry (79 years old), and Albini’s half-brother, British-born Daniel Darlington (35 years old). They can be shared to help with research.

“The terrorists broke into the house, looked for people and then took it,” Perry told CBS News. She said her mother was also at the house and witnessed her father being taken away.

Apleni said her half-brother, Darlington, was in Israel visiting a friend. She said he grew up in the United Kingdom and holds Israeli citizenship through his mother.

“I spoke to him in the morning, around 8 or 9 a.m., and nothing has happened since then,” Albini told CBS News. “He was staying at a friend’s house. The friend asked him not to go out, to close all the doors and windows and stay there. That was the last time they spoke. The friend was not at home.”

The Israeli government press office said on Sunday that more than 100 people were taken hostage by Hamas. American citizens were among the missing, including 23-year-old Israeli-American Hersh Goldberg Poulin, who lives with his family in Jerusalem but was born in California.

He was among dozens of people attending a late-night party in the desert of southern Israel, near the Gaza border, when Hamas gunmen stormed the site.

Hirsch sent his parents two short messages Saturday morning, as the attack began, his father, Jonathan Bolin, told CBS News on Sunday. The first just said “I love you”, and the second just said: “I’m sorry”.

“He was released from [Israeli] Army at the end of April. “He loves travelling, music and festivals. He now works as a paramedic and a waiter to save money for his big trip to India in December,” the father said.

Maj. Gen. (res.) Yisrael Ziv, former head of the IDF’s Operations Directorate and former commander of the Gaza Division, did not clarify the number of Israeli citizens missing or suspected of being held by Hamas.

“These are big numbers,” Ziv said at a press conference. “Very high numbers.”

When asked how Israel would protect the Israeli hostages in Gaza in any counterattack on the densely populated Palestinian territories, Ziv said the military had to strike a balance.

“It is a problem, of course, but we have to do both: on the one hand, deal with the hostages and make every effort to rescue them and release them,” Ziv said. “On the other hand, releasing Hamas is not an option. Israel must do everything to completely destroy Hamas. We have seen who they are – taking children and elderly women hostage – so how can we make peace?”

Ziv said that taking hostages changed the equation for Israel.

“If the attack was just an attack, you could call it a military action. But what they did to the hostages, knowing that our value of human life is different from what they see, that’s the thing that brought us to the point of ‘no going back,’ even if we don’t have the answer. So we have to do what we have to do.”

Emmett Lyons of CBS News in London contributed to this report.