He played down criticism of his administration's response to the hurricane by stating that "the military and first responders. have done an unbelievable job".
Trump has repeatedly blamed the press for what he sees as unfair coverage of the situation.
A few hours after posting her message to Trump, Rihanna called for a "round of applause" for efforts to aid Puerto Rico from former presidents George H.W. Bush, Barack Obama, George W. Bush, Bill Clinton and Jimmy Carter.
San Juan Mayor Carmen Yulín Cruz held a news conference late Friday afternoon and accused the federal government of "killing" Puerto Rico residents with inefficiency.
Cruz, who has personally assisted rescue missions, had responded on Saturday that the focus should be on saving lives. "Many we spoke to on the ground said they don't want to leave - but how can they stay?"
Following requests from Puerto Rico's governor, Trump on Thursday authorized that shipping restrictions, via the Jones Act, be waived immediately for the island over the next 10 days. And the desperate pleas for help that continued Friday from Cruz, as well as other Puerto Ricans in more isolated parts of the country, suggest that far more is needed from the Trump administration's response to the unfolding humanitarian crisis.
"I'd like to begin by sending our thoughts and prayers to the people of Puerto Rico, who have been struck by storms of historic and catastrophic severity", Trump said. "I'm begging anyone who can hear us to save us from dying".
Trump visits Puerto Rico on Tuesday.
His tweets came on the same day that some senior administration officials offered a vigorous defense of the federal response in Puerto Rico at a pair of White House briefings, even as they acknowledged the long road ahead.
The president opened his speech on tax reform with his comments on the federal government's relief efforts in Puerto Rico.
"I just want to hug them", Berrios said.
Long pointed to the "Herculean effort" being made to help the island and its people recover, but conceded: "We got a long way to go".
Mayor Cruz said her goal was to save lives without getting distracted by anything else. "I will continue to do what I have to do, say what I have to say, compliment the people that I have to compliment, and call out the people that I need to call out". "When you're drinking from a creek, it's not a good news story".
"As tone deaf as George Bush's response to Katrina was", Mr. Himes said, "I don't think he would have attacked the mayor from the comfort of a luxury golf club". He's driving the truck to Cleveland so that goods can be shipped to people in need.
A reporter asked her if that had happened to San Juan since her comments Saturday.