REYKJAVIK, Iceland—Rescue teams in Iceland were searching Friday for a small plane that is thought to have crashed while carrying three foreign tourists on a sightseeing trip. More than 500 members of Iceland’s Search and Rescue organization, along with boats, divers, and two Icelandic Coast Guard helicopters, were combing the Thingvellir National Park area in harsh winter weather for the plane, which carried a pilot and tourists from the United States, the Netherlands, and Belgium. The Cessna C172 plane took off from the domestic airport in Iceland’s capital, Reykjavik, on Thursday, for a scheduled two-hour tour. It last made contact with aviation authorities about an hour later. It didn’t send a distress signal. Officials said the plane may have crashed over Thingvellir National Park, a UNESCO World Heritage site about 30 miles (50 kilometers) east of Reykjavik that contains Iceland’s second-largest lake. Asgrimur Larus Asgrimsson, head of operations at the …