Amazon.com Inc .‘s Jeff Bezos has remained largely invisible in the field covered by philanthropy. That changed last week in a single tweet — followed by 42,000 more.

The tycoon’s request to Twitter — asking how he can best use his wealth to help people “right now” — has set off a hysterium of responses from every corner of the world. They include pleas to support health care, education and loan forgiveness, offbeat appeals to back a leather fetish museum in Chicago, plus snarky demands to reboot favorite Tv demonstrates. Even Madonna chimed in, inviting the world’s second-richest man to visit Detroit to engage with charities there.