Self-PortraitistsTaylor Swift, Justin Bieber & More Celebrity Twitter Pictures (PHOTOS)Rachel Osman 07.28.13Self-PortraitistsTaylor Swift, Justin Bieber & More Celebrity Twitter Pictures (PHOTOS)James Franco visits the ‘Veronica Mars’ set, Usher enters the boxing ring, and more of the best shots tweeted by the stars this week.Rachel Osman 07.28.13 8:45 AM ET James Franco visits the Veronica Mars set, Usher enters the boxing ring, and more of the best shots tweeted by the stars this week. James Franco “On the set of Veronica Mars,” tweeted James Franco. The actor will make a cameo appearance as himself in the movie adaptation of the popular television show, which is due out next year. In the meantime, Child of God, a film Franco wrote and directed, will screen at this year’s Venice Film Festival. Taylor SwiftSelena Gomez received many well wishes on Twitter for her 21st birthday this week, including a message from superstar singer Taylor Swift. “Happy 21st birthday to my friend, and the closest thing I've ever had to a sister, @selenagomez!!” tweeted Swift, along with this picture of the two ladies striking a pose. Mario Lopez“Nothing wrong with starting off your day bustin a move with the beautiful @TyraBanks!” said Extra host Mario Lopez. Banks was promoting the 20th season of America’s Next Top Model, which will be the first to feature male contestants. It premieres August 2 on the CW. UsherSinger, dancer, Voice judge, and ... boxer? “Get ready!,” captioned Usher with this picture of him boxing. The Grammy winner is preparing for his role as boxer Sugar Ray Leonard in the upcoming film Hands of Stone. He is taking a break from judging The Voice this fall to shoot the movie and work on other projects. Andy CohenStrike a pose! Watch What Happens Live host Andy Cohen had fun with the Jonas Brothers during their appearance on his show. “Boyband posing with the Jonas Brothers!,” he tweeted. The brothers, including dad-to-be Kevin, will release their fifth studio album, V, in the fall. Gavin RossdaleDoes it get any better than a summer vacation? Apparently not for musician Gavin Rossdale, who shared this picture of himself on the beach. “Coast of Italy,” he tweeted. Jack Osbourne“My little space woman!” captioned Jack Osbourne of this picture with his 1-year-old daughter, Pearl. Osbourne has been extremely outspoken about the recent Rolling Stone cover featuring Boston Marathon bomber Dzhokhar Tsarnaev and started a petition urging the magazine to donate profits from the issue to those affected by the tragedy. Justin BieberThere is no age requirement to be a Belieber! Justin Bieber had fun meeting one of his youngest fans this week, tweeting about the encounter, “She played hard to get. Lol. Cutie.” The superstar, who has been involved in several recent controversies, is currently on the North American leg of his Believe Tour. Adriana Lima“Do you guys like my glasses?” Adriana Lima captioned this Twitter pic. The supermodel and face of Victoria’s Secret, who is mom to daughters Valentina and Sienna, recently left her longtime modeling agency. Ryan Seacrest“Hbd @jlo!,” tweeted Ryan Seacrest along with a picture of himself with the famous singer. Lopez, who received a star on the Hollywood Walk of Fame last month, celebrated her 44th birthday Wednesday. She received another special message in addition to Seacrest’s from boyfriend Casper Smart, who tweeted, “#HAPPYBIRTHDAY to my very very #BeautifulBear.” Eva Longoria“Last day in sound booth for #MotherUp airing this fall on @Hulu!!,” posted Eva Longoria on her WhoSay page. The actress is returning to TV to voice a character in the adult animated comedy, which she also executive produces. Kristin CavallariKristin Cavallari has come a long way since her days on Laguna Beach and The Hills. The former reality star tweeted, “We made it! Mommy/baby LA trip!,” along with a picture of herself and son Camden Jack, who turns 1 in August. Cavallari married Camden’s father, Chicago Bears quarterback Jay Cutler, in June in Nashville.