Avi Schiffmann was almost ready for bed the night of February 28, hours after he attended a protest against Russia's invasion of Ukraine. He was thinking of the thousands of refugees fleeing their country, and he wanted to help. So, the Harvard University freshman and computer whiz sent out the following tweet: "A cool idea would be to set up a website to match Ukrainian refugees to hosts in neighbouring countries." The response was immediate. "People were like, 'Wow, what a great idea, you should do this,'' Schiffmann, 19, tells PEOPLE, "and I was like, 'Huh, maybe I should do this.'" By morning, Schiffmann, visiting a friend in San Diego at the time, contacted Harvard pal and fellow coding expert Marco Burstein for help, he says. "We started talking about the idea and my response was basically, 'I'm in.' From that point on, we basically worked on it nonstop for about three days," says Burstein, an 18-year-old freshman from Los Angeles. "We basically didn't sleep." On March 2, the pair launched Ukraine Take Shelter, where refugees from the war can immediately find hosts with accommodations of all sorts, many accepting family pets. While the pair say they don't have exact figures on how many refugees have found housing, because people don't have to sign up to use the website's services, they estimate they've helped hundreds, possibly even thousands – deduced from the number of listings that hosts have removed once spaces have apparently been filled.