There are 22 scheduled trains per hour that leave Den Haag Centraal on a normal weekday (07:00 - 20:00).
Sprinter services call at every station along the way whilst Intercity trains only stop at the major stations.

There are 6 trains an hour (each way) connecting Den Haag Centraal with Rotterdam Centraal, 6 train an hour connecting it with Utrecht and 4 with Amsterdam.
There are 22 scheduled trains per hour that leave Den Haag Centraal on a normal weekday (07:00 - 20:00). Sprinter services call at every station along the way whilst Intercity trains only stop at the major stations. 
There are 6 trains an hour (each way) connecting Den Haag Centraal with Rotterdam Centraal, 6 train an hour connecting it with Utrecht and 4 with Amsterdam.
Den Haag Centraal railway station