Desperate parents and friends used social media to search for loved ones on Tuesday after a blast killed at least 19 people at a British concert by U.S. singer Ariana Grande, with images of happy-looking teenagers posted next to pleas for help.

"Everyone pls share this, my little sister Emma was at the Ari concert tonight in #Manchester and she isn't answering her phone, pls help me," said one message posted alongside a picture of a blonde girl with flowers in her hair.

Another Twitter user called Erin:P urged people to help him find his sister: "She's wearing a pink sweatshirt and blue jeans. Her name is Whitney."