WASHINGTON: Americans added a quirky step to their voting routine on Tuesday by taking to Twitter and other social media with proof they cast their ballot, amid a drive to boost turnout in the presidential poll.

A study by the Pew Research Centre found that nearly a quarter of registered voters had already announced who they cast their ballot for — or planned to — on social networks flooded with “I voted” posts, clicks and photos.

Wearing aviator sunglasses and a black cap, singer Lenny Kravitz waded into the fray, sticking his “I voted today!” badge on his finger in a photo on his Twitter account.

In the run-up to Tuesday's election, campaigns, celebrities and others have used social networks extensively to try to persuade people to vote and even beat the record 2008 turnout, when two-thirds of US voters cast a ballot.

Facebook itself posted messages at the top of people's news feeds on Tuesday showing users which friends were voting in the election and urging them to do the same by clicking an “I'm a voter” button.

On a separate page, a real-time map of the United States lit up in various areas as soon as a person clicked the button, with a counter clocking-up the hundreds of thousands of Facebook voters.

In its study, the Pew Research Centre found that 22 per cent of respondents in a representative sample of 1,011 adults said they had let people know who they voted or planned to vote for on social networking sites.

The survey also found some 25 per cent of Barack Obama supporters had publicly acknowledged their choice, while 20 per cent of Mitt Romney backers had done so.

Nearly one-third of voters, meanwhile, had been encouraged to vote for Obama or his Republican challenger Romney via posts on social media, while one-fifth had tried to convince others to cast their ballot on social networks.

On Twitter, photos abounded of people proudly sporting their “I voted” badges and some also posted shots of their ballot papers — which is illegal in some states.

Others put up photos of them voting with their children — an initiative backed by First Lady Michelle Obama, who has encouraged Americans to take their kids to polling stations so they get an idea of the workings of democracy.—AFP