RENO, Nev. (AP) — The FBI on Tuesday joined the investigation into the disappearance of a college student who police say was kidnapped from a friend's home over the weekend.

Reno police said while they've been in contact with the federal agency since Brianna Denison was reported missing Sunday, the FBI has now opened its own criminal case and assigned an agent to work with local investigators.

Denison, 19, was last seen around 4 a.m. Sunday when she went to sleep on her friend's couch after a night of partying.

Police Lt. Robert McDonald said drops of blood were left on a pillow she used and a teddy bear her friend gave her is missing. The home's front door had been left unlocked overnight, he said.

Her purse, cell phone and clothing, including two pairs of shoes, were left at the home undisturbed, McDonald said.

Family members Monday night pleaded for help and her safe return. They described Denison as caring and responsible.

"This gives us fear, knowing the type of person she is," Lauren Denison said of her niece. "She would contact us if she could. We adore her and want her back."

Denison is a psychology student at Santa Barbara City College in Santa Barbara, Calif., and was back in her hometown of Reno for winter break.

In the hours before her disappearance, Denison had been party-hopping at venues associated with a weekend snowboarding event, including attending a rap concert at the Sands Hotel and Casino.

Investigators want to talk to a man who dropped off a friend of Denison's at the home that night, McDonald said.

The friend had approached the man at the casino for a ride after the concert, but the man did not come inside the home, he said. The man is not a suspect but is being sought for questioning.

Denison's friend, K.T. Hunter, told the Reno Gazette-Journal that the couch is against the wall of the bedroom where she was sleeping with her dog.

She said she never heard a noise and that the dog never barked.

Hunter said Denison was sober the night she vanished, and had planned to pack Monday to go back to Santa Barbara.

Reno police Tuesday also said there doesn't appear to be a connection between Denison's disappearance and separate attacks late last year on two female students near the University of Nevada, Reno, campus.

Both women were grabbed from behind and sexually assaulted in the early morning hours in November and December. No arrests have been made.