The singer wants to make more people aware of the humanitarian crisis unfolding in Syria, where millions have been left without food, clothing or medical aid as the country's civil war continues.
A post on Williams' website reads, "The worst winter in 10 years and exposure to unspeakable violence is leaving children cold and frightened. With heavy snows, plummeting temperatures and extremely limited food, fuel, clothing and shelter, children are freezing, traumatised and in need of our help.
"The situation is so desperate that for only the second time in Unicef history a level three emergency has been declared. Only when the focus shifts from the conflict in Syria to the humanitarian crisis caused by it will any progress be made. Today you can help achieve this by raising your own voice online."
The Angels hitmaker wants fans to "make some noise for the children of Syria" by sharing the post on their Facebook.com and Twitter.com pages.
The message concludes, "Thank you in advance to everyone who takes action."