"Dear friends, I am pleased to get in touch with you through Twitter. Thank you for your generous response. I bless all of you from my heart," read the tweet, which the 85-year-old pope sent from a tablet at the end of his weekly general audience.
Since the pope last week announced that he would start tweeting under his official Latin title @pontifex, more than 650,000 people have registered to follow his main account in English.
Tens of thousands more are following his Arabic, French, German, Italian, Polish, Portuguese and Spanish accounts.
The Vatican has invited the pope's new Twitter fans to ask questions that the pontiff will try to answer in 140 characters or less.
The first tweet marks a milestone in Vatican communication efforts as it tries to disseminate the Catholic message worldwide -- especially to younger people.
Several leading Vatican prelates are already regular tweeters including Cardinal Gianfranco Ravasi, head of the Pontifical Council for Culture.
"The pope's presence on Twitter is a concrete expression of his conviction that the Church must be present in the digital arena," the Vatican said earlier.
Benedict wants to "ensure that the good news of Jesus Christ and the teaching of his Church are permeating the forum of exchange and dialogue," it said.
Father Antonio Spadaro, director of the Jesuit journal Civilta Cattolica and one of the Church's Twitter pioneers, said the pope's first tweet was comparable to the first papal radio broadcast by Pius XI on February 12, 1931.
"Social media are real places of emotion where people share their lives, their best and worst desires, their questions and their answers," he said earlier.
The Vatican's new communications adviser Greg Burke, a former correspondent for US channel Fox News, said: "We are going to get a spiritual message.
"The pope is not going to be walking around with a Blackberry or an iPad and no one is going to be putting words into the pope's mouth. He will tweet what he wants to tweet."
Several fake Twitter accounts have already been set up in the pope's name and used to mock the pontiff.
Burke said there would always be parodies, as well as tweets that seem official but are fake.
Thousands in the Twitter universe have posed questions to the Church, including a slew of offensive messages about the clerical sex abuse scandals that have rocked the Church over the past decade.
A New York-based mobile advertising startup tweeting under the handle @pontiflex admitted last week that it was not the leader of the world's 1.1 billion Catholics after users mistook its account.
"We are deeply humbled by the surge of new followers today. But if you're looking for tweets from the Pope please follow @pontifex," said the Brooklyn-based company, which has 1,800 followers.
Benedict's 140-character messages will not be written by the pope himself, but by Vatican officials who will submit them to him for approval.
They will then be sent from a single computer -- a safeguard following the embarrassment over the pope's former butler who leaked hundreds of sensitive documents from the Vatican.
The number of followers the pope has accumulated over the past week is still a far cry from the 30 million plus followers on Twitter for pop stars Lady Gaga and Justin Bieber.