Snowmen were sculptures fashioned in the shape of men. They were built of snow, but items were usually added as accessories.
In 1892 London, the Great Intelligence brought snowmen to life to take over the world. The snowmen could be summoned if someone was thinking about them, thanks to being made of telepathic snow, but if said person thought about melting the snowmen, they would melt. This army could be advanced into a humanoid form via the Ice Governess' template. However they were melted en masse when the Intelligence's snow form was melted by the Latimer house's sadness. (TV: The Snowmen)
The remains of a giant alien mosquito defeated by the First Doctor and Steven Taylor combined with snow and the DNA of two human boys, causing the two snowmen they had made with their mother to come to life. They were rescued from being melted by the sun by the Fifth Doctor, who took them to the North Pole. (PROSE: Do You Smell Carrots?)
When the Council of Dead was planning to sell humans into slavery, they caused a massive snowstorm and set up snowmen as sentries. These snowmen could animate, fly and shoot beams out of their eyes to teleport people. (PROSE: Attack of the Snowmen)
Upon exiting the TARDIS, the Sixth Doctor found his coat draped over a snowman, with his umbrella under its arm. Some time later, both the Doctor and Frobisher skidded down a slope before colliding with this snowman. (COMIC: Voyager)
The Demon Magician used his magic to bring to life a snowman. It grabbed John and Gillian, but the First Doctor used his "magic box" to melt the snowman, freeing his grandchildren. (COMIC: A Christmas Story)