Technomancers were precursors to traction-era engineers and mechanics - they existed during the Black Centuries and early Traction Era when technology was considered to be magic, or at least partially so. These people used charms, chants and rituals to help engines run - at least, not until discovering the "half-understood traction technology of the Ancients".
When the Second Traction boom started after London mobolized, technomancers dwindled away, only existing on backward small desert and high ice towns which still used charms and beleived in curses and demons.
They were most popular with the Nomad Empires which had entire regements of technomancers to help keep the engines of their tractions fortresses running.