The LTB is offering an initial three-month contract for the job, which it hopes will span any downturn caused by a war in Iraq.
During the 1991 Gulf War, tourism in London was devastated in the short-term with most Americans refusing to fly to the UK.
"The nervousness surrounding a potential war is already preventing bookings.
We will be asking Londoners to show some civic pride to help out," said a spokeswoman for the LTB.
The marketer will aim to encourage Londoners to support their city by going to West End shows, restaurants and shopping despite fears of terrorism.
The role will report to a committee formed by the London Tourist Board, the Greater London Authority and the London Development Agency.
"We want to promote London for Londoners and will start as soon as we find the right person," said Tamara Ingram, LTB's chairman.
At the same time, culture secretary Tessa Jowell is calling for companies in the travel and leisure sectors to divert cash from their own marketing budgets into joint programmes promoting UK tourism.
Speaking at the British Incoming Tour Operators Association's convention in Edinburgh last week, Jowell said: "If just a few per cent of the industry's current marketing spend was directed to support joint programmes, we could see a vast improvement in productivity and profitability."
The British Tourist Authority is planning to spend £35.5m on marketing Britain this year, but the government is only donating £5m - leaving a shortfall of £30m to be raised from the private sector.
Jowell also called on the tourism industry to share experience and databases to target promotions more effectively.
The call comes as travel and leisure companies are being forced to cut back their own marketing budgets due to a drop in global demand for travel.
UK airlines and operators are experiencing year-on-year sales slumps of up to 25%.