Yes you can! You can duplicate a plan to someone else if the other has a floorplanner account. If you click on the Plans tab you see a green icon behind the name of a plan. Click it for sharing options; At the bottom of the page you get you find that you can collaborate by just filling in the email adress the other person uses for his/her account. The plan will the appear in the plan list of that person and every change either of you save will show up in both plans.
Where is the Plans tab? I see “Ground floor” in the upper left that has a dropdown with my plan in it…but there is no green icon by the name of the plan (only duplicate and delete).