"Cooperative Learning" is a formalized learning structure involves students working together in small groups to accomplish shared learning goals and to maximize their own and other's learning.
I have personally used cooperative (or collaborative) learning in online instruction and the results were positive. I created small groups based on students' areas of interest as well as their availability to "meet" online. Some learning management systems like Blackboard allow you to create group sections so that each individual group has a place to collaborate, share and edit documents, participate in discussions, etc. This is helpful. I also found it helpful for the students to select particular roles that they would play while working in their groups. This helped with a more equal distribution of workload. Some potential challenges include having students who live in very different time zones. This makes synchronous collaboration difficult, but you can easily allow for asynchronous collaboration, too.