Family, friends, and longtime fans of Willie Alexander (above) threw the pioneering Boston rocker a surprise birthday bash Saturday that featured ecstatic performances by the likes of Mission of Burma, the Neighborhoods, Peter Wolf, and Alexander’s own Boom Boom Band. The party at the Davis Square Theatre, organized and curated by Willie’s wife, Anne Rearick, attracted a who’s who from the local music scene, all there to celebrate Alexander’s remarkable career. Still spry and smiling, as always, beneath a tuft of teased silver hair, Alexander joined several of the acts as they played songs he wrote, in some cases, four decades ago. (Alexander, who turns 70 this month, began making music in the 1960s with the Lost, followed by Bagatelle, the Grass Menagerie, the Velvet Underground, and, finally, the great Boom Boom Band, which we were lucky enough to see open for Elvis Costello in 1978.) Other performers Saturday included the Nervous Eaters, the Bags, Preacher Jack, Randy Black, Dennis Brennan, Birdsongs of the Mesozoic, Barrence Whitfield, John Powhida, and Reddy Teddy. Before launching into a frantic cover of “Melinda,’’ Neighborhoods frontman Dave Minehan credited Alexander with inspiring a whole generation of rock ’n’ rollers. “This is like the Kennedy Center or something,’’ replied Alexander. (Governor Deval Patrick wasn’t present but he did issue a proclamation congratulating Willie on “the joyous occasion.’’) Among others spotted on stage or in the crowd were Asa Brebner, Rick Harte of Ace of Hearts Records, former Rat owner Jim Harold, Andrea Gillis, Cal Cali, Mark Kates, the Upper Crust’s Ted Widmer, Greg “Skeggy’’ Kendall, photographer Jon Strymish, Ed “Moose’’ Savage, and Noise magazine publisher T Max.