On the slim chance that anyone reading this is a US resident visiting London, I'm volunteering to contact family members in the states to let them know you're OK. I live and work in NYC.
Please PM me with contact information and something I can tell your family to reassure them the message is from you and not some kind of prank, as i know e-mail queues are ridiculous right now, or if that doesn't work, report any post in General Offspring Discussion and include the information I need in the comments field. Tijs will get the message too, but he's trustworthy.
One of my classmates is studying in London right now and no one has heard from her yet.