How does Dick Frederick find out that Celia has gone off with Rosalind, and what is his reaction?

In As You Like It, Duke Frederick banishes his niece, Rosalind, after he usurps her father’s realm. Initially he allows Rosalind to stay at court for his daughter's sake because she and Celia are like sisters. When he realizes that Rosalind’s presence is reminding the people of her father’s popularity, he banishes her with the threat of death if she stays. Celia, deciding she would rather be with her cousin than her unjust father, goes with her into the Forest of Arden. Two of Frederick’s lords report the young women missing the next morning.
These events occur after a wrestling match between Orlando and Charles, which led to Rosalind’s being smitten by Orlando. Frederick decides that Orlando is responsible for his daughter’s defection and tries to lock him up. The young man has already fled to Arden, so Frederick commands Oliver, Orlando’s brother, to find him and bring him back, dead or alive, within a year. He further orders the seizure of all of Oliver’s property until he completes the mission.