Research Gate is one platform that can help you in this regard. The best strategy to find a co-author is to look for scholars that are interested in your research topics and already have research publications. You can compare your works and decide if the skills and plans suit each other in order to write a manuscript. The other strategy can be to write to the scholars that you are usually citing and also can be cooperative. Surely, there are superstars of your research field that will write only with other superstars. So, do not consider them as potential co-authors. But I am sure there tons of researchers, especially young ones that will be responsive to the new offers. Good luck!
It will benefit both decide your topic and invite other member .literature review , structure design and writing can divide among these and it will save time and article can write in easy way with less time.