Largest online auction house - active users
Who
eBay
What
157,000,000 people
Where
Not Applicable
When

Based on users, the largest auction website is eBay (USA), with an estimated 157 million active buyers worldwide as of 9 October 2015, according to Forbes.

eBay was launched on 4 September 1995 by Pierre Omidyar (France) and has its headquarters in San Jose, California, USA.