Mary may have told her story to only Peter and John or she may have been the spokeswoman for the other women who told the eleven (Luke 24:9), in which case only Peter and John ventured to the tomb. Note that Peter is mentioned first which indicates that he took the initiative in going to the tomb.

Luke 24:9  When they came back from the tomb, they told all these things to the Eleven and to all the others.

In any case, Peter and John were not content to only hear about the empty tomb from Mary; they had to experience it for themselves. We should do the same when others share with us their experiences with the Lord, for there is no partiality with God (Rom  2:11) and His desire is for each of us to experience His Presence.

Romans 2:11  For God does not show favouritism.

Note also how ready Peter and John were to meet the needs of Mary who was distressed over the disappearance of the body of Jesus. We should be just as quick to come to the aid of our friends.

Their quickness was not the only physical thing noted here, but also their speed. They ran to the gravesite, indicating their zeal for doing a good work. We should be so zealous for our Lord and His children!