Since then the Critical Mass has grown a lot and is now the largest of its kind in northern Germany.
There is a 'mass' every last friday of the month at 7 p.m. - the meetup location and other details are posted on facebook, just a few hours before the critical mass. More information and the latest event with the date and location can be found at the official Facebook page . Photos and other references can be found at criticalmass.hamburg, which is hosted by several criticalmass-enthusiasts who explicitly states that they have nothing to do with the announcement of the meetup location or other organisational activities.
The first Critical Mass bike ride in Hamburg was on March 31, 2000 with 15 cyclists. The meeting point at that time was 5 p.m. at the metrostation St. Pauli. Participation in the years from 2000 to 2003 was moderate. Up to 40 cyclists took part during this period. 
On July 3rd, 2009, 250 bike riders participated a Critical Mass through Altona, the center of Hamburg and St. Pauli.
The latest numbers from summer 2012 are well above a thousand riders! The police has counted 1200 riders in August 2012, others say it were about 2000 riders.
In April 2014 a new peak was recorded with 4500 riders.