The airport has set up a log cabin in the departure lounge at the Docklands airport, open for two weeks until 19 December, where passengers can record their messages.
It opened last week, and the airport has now created a video to promote the campaign with footage from the cabin.
The airport has also provided gifts for some visitors, with prizes including eight pairs of tickets across four airlines and gifts donated from concession partners such as the duty free stall.
Charlotte Beeching, head of comms, said that in the past the airport had focused more on traditional PR.
She added that this online approach was a new direction and that the airport hoped to achieve organic growth with people sharing the video online.
The airport will also hold a competition on social media later this week to help promote the film, encouraging people to share the video in order to win a hamper.
Passengers have recorded between 200 and 250 messages so far, which are then uploaded on to a microsite and the sender receives a unique code to access and share the message.
Declan Collier, CEO at London City Airport, said: "Not everyone can be with their family or friends this Christmas. People often send ‘Across the Miles’ cards but we wanted to give passengers the chance to create live messages and have a bit of fun at the same time, creating a really festive atmosphere in the terminal."
Watch the film here: