The men approached the man at about 1:40 p.m. Monday in the 7600 block of Melrose Avenue, near Stanley Avenue, while he was walking with his girlfriend after he dined at a nearby restaurant, police said.
The men assaulted the man and demanded his property, police said. One suspect pulled out a gun and took the man's belongings, including a gold necklace before fleeing with the other two suspects in a red-four door sedan driven by a fourth man.
The three men who committed the assault are described as being between 20 and 30 years old. A description of the driver was not available.
Anyone with information on the robbery can call Wilshire Robbery Detective S. Azmy at 213-922-8229. Calls during non-business hours or on the weekends can be made to 877-527-3247.
Anonymous tips can be called in to Crime Stoppers at 800-222-8477 or submitted online at lacrimestoppers.org.