Star Tracks: Thursday, August 4, 2011

Jennifer Hudson wishes President Barack Obama a happy 50th birthday Wednesday at Chicago's Aragon Ballroom for a Democratic National Convention fundraiser with Mayor Rahm Emanuel.

Buffer than ever, Kellan Lutz gets pulses racing Wednesday, doffing his shirt for a beachside run in L.A.

After a romantic New York cruise with Leo, Blake Lively gets back to work Wednesday, filming a sundrenched scene for Gossip Girl's fifth season in Santa Monica, Calif.

Carry on! Pete Wentz hits a Beverly Hills shopping mall on Wednesday holding his most valuable possession – two-year-old son Bronx.

Newly single Kate Bosworth has a case of the blues – hair color, that is! – while hitting a Coldplay concert (sponsored by Samsung and ATampT) in L.A. with new beau, director Michael Polish, on Wednesday.

Bethenny Frankel brings her own neon spotlight to celebrate the launch of her new SkinnyGirl Sangria cocktail at New York's Gramercy Hotel on Wednesday.

Rachel Weisz makes a fast break into New York City's JFK airport with son Henry, 5, and new husband Daniel Craig.

Justin Bieber lets his potty-mouthed tee do the talking Wednesday while shopping on Los Angeles' Melrose Avenue.

After attending the premiere of The Change-Up, Sandra Bullock attends to her main man, 18-month-old Louis, in L.A. on Wednesday.

Emma Stone stops traffic in another peek-a-boo black dress Wednesday while arriving at the Late Show with David Letterman studios in New York.

Leaving her pampered pooch at home, Cowboys and Aliens star Olivia Wilde shows off her Pink Floyd love Wednesday in Los Angeles.

Sheryl Crow makes friends with one cuddly critter, sea lion Clyde, during a visit Wednesday to SeaWorld in San Diego, Calif.

Usher wheels a double bundle of cuteness – sons Naviyd, 2, and Usher V, 3 – during a sunny stroll in New York City on Wednesday.

Amanda Seyfried keeps it casual in flip-flops Wednesday in between shooting scenes for her latest movie, The Wedding, in Greenwich, Conn.

Looks like those workouts are paying off! Ashley Tisdale shows off her fit form as she heads into a West Hollywood gym Wednesday.