LONDON — On city streets strewn with ash, and in social media posts heavy with concern, the family members of those who lived in London’s Grenfell Tower pleaded on Thursday for information about loved ones still missing one day after a devastating fire.

“My mum is missing — Sheila, 84 years old, 16th floor of Grenfell Tower,” wrote Adam Smith on Twitter.

“Please help us find Mohammad Alhajali … His family are worried sick about him and his brother is in hospital,” Mirna Suleiman, wrote on Facebook about a Syrian refugee who was unaccounted for. Another friend later confirmed that Mr. Alhajali was killed in the blaze.