The parents of 10-month-old Lisa Irwin reported her missing in Kansas City Tuesday. They claim she was snatched from her crib in the middle of the night.
A family member told a news station that the FBI is looking at surveillance video of a couple in California with a very young child.
He did not give any other details.
Experts said it's rare for strangers to kidnap infants, but when they do, it's often because they want a child of their own.
Irwin's parents deny they were involved with her disappearance.
Saturday, a family spokesperson said Irwin's parents are setting up a reward, hoping it could help lead to information in the case.
The spokesman also said the parents will be giving fewer media interviews, because they want full attention on finding their daughter.
Police have not named suspects or solid leads in the case.
The Associated Press contributed to this report.