Jeff Bezos, one of the world’s wealthiest business leaders, hasn’t given big sums to charities yet, but he signaled today that he is ready to do so — and made clear that he is more interested in giving money to charities that directly help people in desperation than in building institutions that will last for generations.

The announcement came in an unusual way: The Amazon founder posted a tweet soliciting advice on where to concentrate his philanthropy. Mr. Bezos’s open-source call for ideas did not provide clues to how much he will eventually donate or when, but he asked what people thought about the value of helping people who are currently in need.