Participation of multiple researchers in our project
Since professors of CS are often looking for collaborative tools for their students, you might be able to use them as a resource. The ACM has a special interest group for educators, SIGCSE, that maintains a mailing list of members. It frequently gets requests for research participation, so you might try to send a message there, though it requires membership. Other professional organizations may have some similar special interest groups that can be contacted. 

Should you find a huge number of collaborators testers of your collaborative systems I wouldn't think that co-authorship would be necessary in most cases, though you might want a fairly long acknowledgement section in your paper. It would depend, of course, on how much they add to your work.