Kaká, Van der Vaart, Granero and Marcelo have to be found at Savetherealgame.com.
Users who complete the game get the opportunity to win a trip with the Real Madrid players in their team plane to a La Liga game.
Fans must release the players by playing a game where they have to find four numerical codes hidden on the internet. Kaká, Van der Vaart, Granero and Marcelo will help players on their mission with different hints and tips. The answers to the questions will be revealed during the game.
The game aims to mark the occasion of the upcoming Real Madrid – Barcelona game that will take place at the Santiago Bernabéu stadium next month.
Last month, the online gaming company, which also sponsors Italian football team AC Milan, appointed Universal McCann to handle its UK media-planning and buying account.
The Austrian-based gaming site, which has 20 million registered users in markets including Germany, Spain and Italy, is expected to spend around £4m on radio, print and online advertising in an attempt to secure a presence in the competitive online gaming market.
