Police in the northern California town of Tracy say they've received some 600 since Sandra was first reported missing a week ago after she went outside to play.
More reward money is being offered as well, with the amount offered by Tracy Crime Stoppers and the Carole Sund/Carrington Foundation for the girl's safe return now more than $22,000.
Meanwhile, police say they will send a T-shirt recovered in a waste facility out for further testing.
Searchers had thought the pink shirt was the one Sandra was wearing when she disappeared, but her mother says it's not the same T-shirt.
Crews are expected to continue searching trash in the waste facility through Saturday.
Investigators are also searching nearby rivers and reviewing surveillance video in hopes of finding Sandra, reports Early Show national correspondent Hattie Kauffman.
Police have also questioned Sandra's father, Daniel Cantu, who just returned from Mexico. But he told reporters he hasn"t seen Sandra in a year, and has "no problem" with taking a lie detector test.
Detectives have also spoken with this Frank Wohler, a neighbor who admits he kissed the second-grader on the lips two years ago. It was, Wohler says, an "impulse -- just being friendly. I do that to some of my students, also."
FBI agents and Tracy police have searched nearby homes and towed vehicles to test for evidence. Tracy Police Lt. Jeremy Watney observed that, "The quality of the leads that have come in have investigators upbeat that we'll have a conclusion of this case shortly."
Sandra's image is everywhere in the small community of Tracy, and residents are continuing nightly vigils, hoping their thoughts and prayers are answered soon with her safe return, Kauffman notes.