"No one deserves this," says Mark Lewis, a friend of Alexander Pinczowski, who is missing along with his sister, Sascha

A good friend of the New York brother and sister who are missing after Tuesday’s deadly terrorist attacks in Brussels says the family is doing everything it can to get some answers.

“The waiting is really, really difficult,” Mark Lewis told PEOPLE Wednesday afternoon. “It’s an absolute nightmare.”

Sascha and Alexander Pinczowski were getting ready to fly back to New York when the first bomb went off in Zaventem airport’s departures hall.

“After the explosion we haven’t heard from them,” the Netherlands-based Lewis told PEOPLE earlier Wednesday. “We tried all hospitals with no luck. Their mom was the last to speak to them, but their call was cut off after the explosion.”

Lewis, who has been friends with Alexander for five years, described him as an “incredibly friendly, dog-loving person” who has lots of friends and loves to cook.

“He posts photos of dogs on Instagram. It’s a hobby of his but he has a big following,” he said. “They are sweet and wonderful people.”

Alex’s girlfriend, Cameron Cain, has also posted pleas for their safe return on social media.

Lewis also hopes Sascha and Alexander, who “are very close,” are found soon.

He added that “the family is absolutely devastated.”

“What would you imagine if your two kids were at the site of a terrorist attack and you hadn’t heard from them?” he also said. “A family friend was quoted in a newspaper saying the mother is worried sick, and indeed that’s the case.”

Two explosions at the airport killed 14 people and injured nearly 100. A second attack at a Maalbeek Metro Station around an hour later killed 20 people and injured at least 106.