The fact that the other apostles are mentioned suggests that they were also involved in speaking to the people and that it was not just Peter who did all the speaking. Most likely, if the events took place in the upper room where the apostles were meeting (Acts 1:13; Acts 2:1) or in the street immediately outside, then, besides Peter's speech, there would have been lots of individual conversations between the Twelve and different people taking place.
37 Now when they heard this they were cut to the heart, and said to Peter and the rest of the apostles, “Brothers, what shall we do?”