LONDON (Reuters) - WPP , the world's biggest advertising company, said it would target flat organic growth and profit margin in 2020 after weakness in major markets dragged its fourth quarter down. The British group reported a 1.9% drop in its main measure of organic revenue less pass-through costs compared with the 0.5% growth recorded in the previous quarter. For the year, the group reported organic sales down 1.6%. That excludes its data business Kantar after it sold a major stake in the unit..