In Act 4, Abigail Williams and Mercy Lewis have been gone for 3 days. Where does Parris think they gone?
I think that Parris' lack of answer on this question is what ends up feeding his own insecurity. The fact that he cannot formulate a full explanation as to where Abigail and Mercy have gone helps to erode his once strong and confident foundation. He hears some small rumor of the fact that the girls might have gone aboard a sea vessel from his daughter, but that's really all he has. He has little idea as to where both girls are and this strikes at his own fear and doubt. He based everything he did in terms of rallying the town regarding the fear of witches based on Abigail's persuasion and her own testimony. As she is gone, Parris understands that a major element of both the case for witches in Salem and his own credibility has gone with it and in this, there is a sense of fear. It is for this reason that he really lacks a clear answer as to where both Abigail and Mercy have gone. All he knows is that their disappearance does not spell good things for his own case and his standing in Salem. Given the girls' disappearance and the rebellions in Andover, Parris knows that his own time in Salem is coming to an end, the only answer he can ascertain at this point in the drama.
At the beginning of Act Four, Deputy Governor Danforth asks Parris what is troubling him, and Parris responds by saying that Abigail and Mercy Lewis have been gone for the past three days. When Danforth responds by saying that he will send out a search party for them, Parris mentions that he thinks they may have boarded a ship. Parris elaborates on his suspicion that the girls have boarded a ship by saying that he overheard them speaking about it last week. Parris then tells Danforth that Abigail has stolen thirty-one pounds from his strong box, leaving him penniless. Parris believes that the girls fled Salem because they feared there would be an uprising similar to that of Andover. In order to avoid the town's wrath, the girls stole Reverend Parris's money and possibly boarded a ship leaving the colonies. It is interesting to note that Parris does not feel guilty for the deaths of the innocent citizens, and is entirely concerned about his own well-being. He is not so much concerned with Abigail and Mercy's disappearance than he is with the fact that his money was stolen. He also urges Danforth to pardon Proctor and Rebecca Nurse in order to avoid being harmed by an angry mob.