Startup Idea : Find people who want to do the same

My app will allow users to post activities, which they are going to do and they need some people to join them. So users can post their activities with proposed time and place and others can find it through categories and join them. The person who proposed the activity can see the profiles of users who joined their activity and they can approved them or decline them. It will have a few filters so activities wil only be displayed to relevant people.