Stolen Beverly Hills Dog -- Hilary Duff & Celeb Posse Scour City

Hollywood's all about who you know ... even for dogs, because Hilary Duff, Lance Bass, George Lopez and others are tearing up the town to find a Beverly Hills icon -- who happens to have 4 legs.

Owner Julia Cohen says her pooch -- Charlie -- was stolen Wednesday, and when the news hit social media ... stars like Duff spent all night driving around on the hunt. Others like Lea Michele searched on foot.

Julia says her little guy's a fixture outside Switch -- her popular BH boutique -- and security footage shows he was stolen by a pregnant woman.

The reward for Charlie is currently $5,000 and growing. If you have info. on him please contact Switch at (310) 860-1650.