PORT-AU-PRINCE, Haiti—U.S. officials are working with Haitian authorities to try to secure the release of 12 adults and five children with a U.S.-based missionary group who were abducted over the weekend by a gang notorious for killings, kidnappings and extortion. The group was snatched by the 400 Mawozo gang, which controls the Croix-des-Bouquets area east of the capital of Port-au-Prince, police inspector Frantz Champagne told The Associated Press on Sunday. The abduction happened Saturday in the community of Ganthier, which lies in the gang’s area. It was blamed for the kidnapping of five priests and two nuns earlier this year. As authorities sought the release of the 16 Americans and one Canadian with the Ohio-based Christian Aid Ministries, local unions and other organizations expected to launch a strike Monday to protest Haiti’s worsening lack of security. The Western Hemisphere’s poorest nation is again struggling with a spike in gang-related kidnappings …