Money raised from the benefit concert at St James Piccadilly in central London at 7.45pm will go to the British Red Cross Family Tracing Service.
The event, plus a preceding church service at 6pm, will mark International Day of the Disappeared, a United Nations-led initiative to highlight the plight of those missing because of war, unrest or migration.
Associate rector, Rev Lindsay Meader told Premier: "Some of them have literally 'been disappeared' by tyrannical regimes; loved ones are arrested or detained and nothing further is heard from them.
"Others, of course, have fled their countries with very good reason. Many have been separated in the journey and in that chaos...
"There's also ambiguous loss, which is those who are separated from their loved ones and simply don't know what's become of each other.
"We want to do something to highlight the plight of these people and to make the situation more widely known and understood."
The Citizens of the World Choir (pictured top), a group open to refugees, migrants and asylum-seekers, and the Scottish actor David Robb are taking part.
Rev Meader urged people to "pray not just for all those literally nameless and faceless to us but perhaps, inspired by some of those case studies and real life stories, to think through the particular situations and places that people find themselves in and pray for people who are going through that even as we speak."
A free, impartial and confidential service, the British Red Cross Family Tracing Service has been operating for more than 100 years.
Click here to listen to Premier's Alex Williams speaking with Rev Lindsay Meader: