President Obama is jump-starting his outreach to young Americans with a targeted campaign aimed at enlisting new campaign volunteers and helping register first-time voters.

The initiative, which the campaign has branded Greater Together,  is part of Obama’s strategy to grow the pool of eligible voters and maximize participation in 2012 among the same key constituencies that propelled him to victory four years ago.

Aides launched the effort through a new website , messaging blast through social media, and a web video in which Obama speaks directly to his young supporters.

“Four years ago the cynics said that young Americans were apathetic, that you didn’t care about the direction of this country or have what it takes to change it. But that’s not what I saw,” Obama said. “You proved them wrong by helping to build a movement for change.”

Obama cited the full withdrawal of U.S. troops from Iraq by the end of the year, repeal of “don’t ask don’t tell” and health insurance and financial regulatory reforms as accomplishments that young Americans might particularly appreciate.  He also asked viewers to make a commitment by signing up online.

“There are lots of things we don’t know about next year’s election. But something I’m completely sure of is this movement needs you in it,” Obama said.

Obama campaign manager Jim Messina said the record engagement of American voters ages 18 to 29 in 2008 was “game-changing” and will be “defining issue” for 2012.

The campaign has appointed two new aides to spearhead outreach to younger Americans, nonprofit youth advocate Valeisha Butterfield-Jones and former Obama field organizer Eric Zoberman.