A social-media campaign that took off on March 2 has generated thousands of reservations across the country, even as invading Russian forces ​​indiscriminately shell civilian neighborhoods in cities like Kharkiv, Chernihiv, Mariupol and Sumy.

The goal is to get money into the hands of Ukrainians on the ground as quickly as possible, said Rob Meehan, an Airbnb host with properties in Guadalajara and Puerto Vallarta, Mexico, who took part in the grass-roots effort.

Mr. Meehan logged on to the Airbnb platform Friday morning and typed in “Ukraine.” When an apartment popped up in the capital city of Kyiv, he booked it for the first available two nights, for a total of $229.

“Like a lot of other people, I’ve been feeling the stress of this. All of the sadness that is going on over there,” he said Friday.