Peter not only preached the gospel on the Day of Pentecost. In the very next chapter, Acts 3, after the healing of the lame man at the gate Beautiful, Peter again preached the gospel.

"The God of Abraham, and of Isaac, and of Jacob, the God of our fathers, hath glorified his Son Jesus; whom ye delivered up, and denied him in the presence of Pilate, when he was determined to let him go. But ye denied the Holy One and the Just, and desired a murderer to be granted unto you; and killed the Prince of life, whom God hath raised from the dead; whereof we are witnesses." - Acts 3:13-15 KJV

Peter than told them how they must obey the gospel.

"Repent ye therefore, and be converted, that your sins may be blotted out, when the times of refreshing shall come from the presence of the Lord;" - Acts 3:19 KJV

What was the result?

"And as they spake unto the people, the priests, and the captain of the temple, and the Sadducees, came upon them, being grieved that they taught the people, and preached through Jesus the resurrection from the dead. And they laid hands on them, and put them in hold unto the next day: for it was now eventide.

“Howbeit many of them which heard the word believed; and the number of the men was about five thousand." - Acts 4:1-4 KJV