One could argue that it is the girls who are most to blame for these events. It was their questionable activities in the woods that prompted Betty Parris and Ruth Putnam to become ill and spark the investigation into witchcraft. Further, it was Abigail to accused Tituba -- a slave who seems only to have confessed in order to avoid beatings or death -- and then Abigail and Betty who piled accusation upon accusation in the final moments of Act One. Finally, it was the girls who knowingly accused innocent people in the court.
One could also argue that it is Mrs. Putnam who is most to blame because she sent her daughter, Ruth, to Tituba to conjure the spirits of Mrs. Putnam's dead children in order to find out how and why they died. Her action then led to the events above.
One might also argue that it is the adults who believe, or purport to believe, these children: adults including Reverend Parris (who purposely hides the truth about what he knows from the court in order to maintain his reputation and position), Mr. Hale (who recognizes early on that the court was erring and condemning people to die based on little else besides the testimony of children, but says too little too late), Judge Hathorne (who seems more interested in using the trials as a way to increase his own power in the community and colony), and Deputy Governor Danforth (who adopts the position that these girls are speaking for God and who refuses to delay executions even when there is compelling evidence that the girls were dishonest because it would undermine his own authority). One could even suggest that John Proctor is to blame because Abigail tells him much of the truth about the forest early on, and he says nothing until it is too late.
There are a great many people to blame for these trials, and it seems to me that they could not have occurred without all, or at least most, of these people acting as they did. The girls lied, yes, but it was up to the adults to decide how to respond, and they responded wrongly. Some were too willing to believe in the lies -- like Mrs. Putnam -- and others seemed to have something to gain in their perpetuation -- like Mr. Putnam, Parris, Danforth, and Hathorne. All are responsible.