Timbaland was the subject of a manhunt yesterday after his family believed he was so distraught over the theft of a $2 million piece of jewelry he might harm himself ... this according to law enforcement sources.

According to sources, the L.A. County Sheriff's Department put out a "possible suicide attempt" APB just before 5 PM PT yesterday. A helicopter and squad cars went on the hunt for the rapper/producer's Escalade.

Here's what we're told happened ... Timbaland was on the phone earlier in the day with his brother-in-law ... deeply upset about something. We're told one of the things that was eating at him was a theft at his Malibu residence a day before. Someone had stolen a crazy expensive Jacob & Co. watch -- valued at $2 million -- and Timbaland suspected it might have been someone he trusted.

Timbaland left his home yesterday and began driving. Family members couldn't locate him, became extremely worried and called the Sheriff's Department.

We're told the helicopter located the Escalade, ground crews pulled Timbaland over and began talking to him. At some point they put Timbaland in a patrol car and took him to his residence, where they continued speaking with him and family members.

Deputies called for paramedics to come and evaluate Timbaland. After the evaluation, paramedics determined Timbaland was not a threat to himself and left.

We're told the Sheriff's Department is investigating the theft of Timbaland's jewelry and they have possible suspects.

Timbaland's rep could not be reached for comment.