Officials were joined by Yeoman's parents and extended family, some of whom traveled from out of the state to be in Yuba City Friday.
Yeoman's family stood around Gridley Biggs Police Chief Dean Price as he read their statement. In it, the family says they still believe the 20-year-old is alive.
"We firmly believe, in our hearts, that Aly is alive and needs our help," the statement read.
Sutter County Undersheriff Jeff Pierce said investigators are looking at messages Yeoman sent to family members around the time of her disappearance, but didn't go into further detail.
Yeoman was reported missing on April 1, but was last seen March 30 at a friend's house in Yuba City. Her truck and cell phone were found at an orchard in Live Oak late Monday. Investigators served a search warrant Thursday at that home in Yuba City.
Police would not say if foul play is suspected and didn't comment on rumors of ransom messages.
The FBI announced a $5,000 reward for information leading to Yeoman's safe return.
The Sutter County Sheriff's Department, which has taken over the case, has established a tip line. Anyone with information about where Yeoman may be is asked to call (530) 822-7307.