The deal, for an undisclosed fee, will eventually place social networking facilities from TripUp directly into the portfolio of Sidstep sites, including its UK & Ireland operation.
TripUp allows travellers to post blogs, reviews, photos, maps and video onto the site.
The development comes just weeks after Sidestep created one of the first Facebook applications for members to plot their previous and upcoming trips..
Sidestep chief executive Rob Solomon said: “The sheer number of people using community and social networks demonstrates that these sites are becoming a more important part of today’s digital lifestyle.
“This acquisition allows Sidestep to quickly introduce millions of travellers to TripUp’s innovative features and furthers our goal of redefining the way people find and use relevant travel information.”
The deal also demonstrates the speed in which social networking sites are being snapped up by existing web companies.
TripUp was launched just ten months ago in the US.
TripUp chief executive Sam Rogoway added: “TripUp revolutionises social networking for travel and proves that online travel communities don’t need to be static or boring.
“By joining the Sidestep family and collaborating on new innovations, we’re poised to introduce our exciting community and social network to millions of travellers.”