The "little flock" illustration is part of a large sermon Jesus gave to "a crowd of so many thousands." (Luke 12:1) It covers the entirety of Luke chapter 12.
In verses 1 to 21 Jesus addresses the crowd.
In verses 22 to 40 he addresses his disciples (whom we can assume are the twelve, though it could have included others).
In verse 32 Jesus says, "Have no fear, little flock, for your Father has approved of giving you the Kingdom." He then continues the illustration by emphasizing the need for readiness in anticipation of the Master's return.
At verse 41 Peter asks Jesus, "Lord, are you telling this illustration to us or also to everyone?"
This is an interesting question for Peter to ask, because it suggests that Peter felt Jesus' audience may not have been limited to just the twelve, and that those among the "crowd of so many thousands" may have also been Jesus' intended audience for the "little flock" illustration.
Instead of giving a direct answer to Peter, Jesus' response in verses 42-53 is broad and very telling: "Who really is the faithful steward, the discreet one, whom his master will appoint over his body of attendants to keep giving them their measure of food supplies at the proper time?"
Then at verse 54 Jesus addresses "the crowds" again. What he tells them directly correlates with what he had just said to the disciples moments earlier about the necessity of diligence and readiness, and the cost of negligence and unreadiness. See verses 45-46 where he tells his disciples the illustration of the consequences of bad stewardship, and then compare verses 54-59 where he likewise tells the crowds another illustration about the consequences of bad stewardship.
The answer to Peter's question seems to be clear: Jesus' "little flock" illustration was meant for, and applicable to, the disciples as well as the crowds.
This ultimately suggests that anyone who "takes the lead" by undertaking the responsibility to shepherd God's people is a "faithful steward, the discreet one." And with that responsibility comes tremendous accountability.