Larger travel companies have also joined the effort to offer facilities and services to refugees. Airbnb, in partnership with its nonprofit arm Airbnb.org, has been working with hosts to supply free temporary housing for up to 100,000 refugees fleeing Ukraine to neighboring countries like Poland, Hungary and Romania.

Thousands of people around the world have also booked and paid for Airbnbs within Ukraine, with no plans to travel there, in efforts to send money to Ukrainian homeowners. Between March 2 and 3, more than 61,000 nights were booked in Ukraine, 34,000 of them by people in the United States, the company reported.

Paige Holden, 43, an interior designer from Los Angeles, was at first skeptical about the initiative, concerned that if she booked an Airbnb property the hosts would not be able to access the funds. But after reaching out to some of them and seeing their desperation, she immediately booked an apartment in a Kyiv property, which sent $4,700 to a family of five.

“After I sent out an inquiry, a woman in Kyiv sent me a picture of her three young children, huddled in a cold, dark basement filled with other distraught families,” Ms. Holden said.

“You have to remember that these people lost everything overnight, their homes, their incomes, they have nothing left but to fight for their lives,” she said.

Over the past week, Benjamin Wagner, 27, a part-time tour guide and history student based in Berlin, has been driving refugees from that city’s central train station to host families across the city, volunteering through a WhatsApp group.

“At this time, it doesn’t matter where you are from, what you do or where you work,” Mr. Wagner said. “We all have one collective responsibility to help our Ukrainian brothers and sisters. This humanitarian crisis affects us all, and tomorrow we could be in their shoes.”