There's already great answers there from @JanVladimirMostert and @fibric , hence I'm not going to repeat everything. But I'm surprise the classic whiteboard is mentioned only once. Like Jna, most of the time it's a "in the head+paper" drafts, but it then very quickly move to the whiteboard, even before using it to share the ideas, but because of the ease of erase/redraw and how quick it is to setup things on a whiteboard. Usually, once we have a rough idea, we start talking with other engineers (no big meeting, just a dialog with another guy to challenge the ideas). And that's where the whiteboard is really helpful, because it's a great support to explore the different challenges.
For the second part of @sandeep 's original question: how to work remotely, in the past (as of today I'm no longer working with remote teams that much) we make intensive work of Confluence - for storing and text - and Visual Paradigm for the diagrams. Visual Paradigm - once you're used to it - make diagram creation really a quick task, so we had some screen-sharing conference with live discussions and edition of the diagram.
If you want to give it a shot, I believe the Community edition (free for non-commercial purpose only) is still available, it could help you see how it could fit your need.
For simpler diagrams, Lucidchart was enough and does the job well.