Late in the 1800's the Pope himself proposed a particular monthly intention for the Apostleship of Prayer, and since 1929 the Holy Father has also given a specific mission intention to the faithful for their prayerful attention.
On its 100th anniversary in 1944, Pope Pius XII gave thanks to God for the Apostleship of Prayer, calling it "one of the most efficacious means for the salvation of souls, since it concerns prayer and prayer in common." He commended the organization for its goal: "to pray assiduously for the needs of the Church and to try to satisfy them through daily offering."
Pope John Paul II, on the occasion of its 150th anniversary in 1994, wrote: "As the dawn of the third millennium approaches a world in which many sectors have become quite pagan, it is obvious how urgent it is for members of the Apostleship of Prayer to be involved in the service of the new evangelization. For Christ has come to preach the Good News to the poor, and the Apostleship of Prayer has always considered itself a form of popular piety for the masses. As such it has performed an important service during the past hundred and fifty years by giving new life to people's awareness of how valuable their lives are to God for the building up of His Kingdom."
Truly the Apostleship of Prayer is the Pope's own "prayer group." It is, as Pope John Paul II wrote in 1985, "a precious treasure from the Pope's heart and the Heart of Christ."
The Apostleship of Prayer has renewed itself for the contemporary world. Pope Francis himself has approved the renewal document published by the international office of the Apostleship in Rome. It’s now available at this link.