How do I find researchers to collaborate with online? I am looking for researchers with whom I can collaborate online. Some ideas are hard to implement by one person. So, how can I find and cooperate with other   research students from other universities online?
First, you need to clearly identify your field of interest (for instance, Bayesian meta-analysis of clinical trials).

After that, it is up to you and your time and resources. These are some suggestions:


Look at other SE websites and visit the profile of leading
contributors (eg CV);
Check recent and impactful scholarly papers, retrieve
the email of the corresponding authors, and write to them (eg Chatterjee et al, JAMA Neurology 2013); 
Look at
leading academic institutions in your field, and write emails to
selected contact people (eg David Spiegelhalter at the University of Cambridge);
Ask a local or nearby opinion leader for key selected contacts.


You need to clearly state your goals, your expertise, and your commitment, and then see if these fit. Try multiple times and multiple venues, eventually I am sure you will be able to create a fruitful collaboration.