There are 100 missions in total; 20 in Ibiza Area 1, 20 in Ibiza Area 2, 15 in Hawaii Area 1, 2, 3 & 4.
You can check your overall completions of the missions by going to the Start Menu , going to the "Progress & Objectives" menu, going to the "Discovery" tab by pressing and selecting "Events". The Missions on your map are represented by a bomb icon.
If you cannot see any missions on your map, try reloading the game from the dashboard or just simply wait for them to pop up. Some are time specific and won't appear during some times.