Bo Albertus, a school principal in Denmark, finds the Spanish raisins he now snacks on less tasty than his favorite Sun-Maid ones from California. There is no perfect substitute for Heinz tomato soup, a staple in his pantry. And he misses Pepsi Max.

But as long as President Trump pursues policies that Mr. Albertus, 57, believes put Europe’s economy and security at risk, he will boycott these and other U.S. products. He is one of a growing number of Europeans, Canadians and others who are forgoing American goods to show their anguish and dismay at Mr. Trump’s treatment of longtime allies.

“I felt a sense of powerlessness,” said Mr. Albertus, who is an administrator of a Danish Facebook group dedicated to boycotting American goods that has 90,000 members. “We all feel that we are doing something,” he added. “We are acting on our frustration.”

The strongest momentum behind such consumer action appears to be in countries that Mr. Trump has directly antagonized, like Denmark, whose territory of Greenland he has threatened to take, and Canada, which he has repeatedly said should become America’s 51st state.

But as Mr. Trump embraces President Vladimir V. Putin of Russia and imposes tariffs on European goods, groups dedicated to boycotting U.S. goods and swapping tips on local alternatives have popped up in several European countries.

In a Swedish Facebook group with over 80,000 members, users ask for tips on buying non-American laptops, dog food and toothpaste. Members of a French group sing the praises of European laundry detergents and smartphone apps, and debate whether Cognac or Scotch whisky is the better alternative to bourbon.