Tuesday marked a solemn day for the family and friends of Lauren Spierer, the Indiana University student who has been missing since June.Her parents and sister posted a message to her on Facebook for her 21st birthday."Remembering today, 21 years ago, as one of the happiest days in our lives," the family posted on Facebook. "Happy birthday, Lauren. We love you with all our hearts." Special Section: Lauren Spierer Spierer's parents did not return to Bloomington this week and chose to forgo a vigil or prayer service."To know that today is her birthday, and it's a day of sadness instead is just so painful for everyone," said Rabbi Sue Silberberg with the Hillel Jewish Center, where Spierer worshiped. "Her family is suffering so much."Those supporting the effort to find Spierer sent messages about her on Twitter, urging anyone with information to step forward and expressing regret that she will not be with her family for the milestone."Sending you love as we celebrate your birthday," read a tweet from @NewsOnLaurenS. "We will celebrate you every day until you come home."Spierer disappeared in the early-morning hours of June 3 after a night of drinking with friends.Volunteers spent months searching for the student, and investigators from numerous agencies have spent countless hours trying to find out what happened to her."All of us who've been involved in the search have just suffered so many hours of grief," Silberberg said. "Please, please, please help to put her family out of their grief so they know and they can go forward and they know where Lauren is. Somebody out there knows where she is."There have been no arrests in the case.Investigators asked anyone with information about Spierer's disappearance to call them at 812-339-4477.