Justin Bieber's Instagram Post About Selling His Home Has Attracted Multiple Buyers

Justin Bieber's personal Instagram may be more effective than the Multiple Listing Service in moving real estate ... because his one post declaring he's in the market to sell his house has generated tons of interest ... including from at least one billionaire.

Bieber -- who boasts an insane 120 million followers on IG -- casually mentioned last week he's looking to sell his Beverly Hills home ... "I'll sell it with all the furniture. MAKE AN OFFER."

Sources with direct knowledge tell TMZ ... Justin's been contacted by at least 5 prospective buyers ... either directly or through their realtors. We're told one of the prospective buyers is a billionaire from a very famous family.

Justin and Hailey bought the 6,132-square-foot property last year for $8.5 million. A highly respected real estate agent in L.A. tells us the home isn't worth more than that -- but says there are certain buyers who will pay a premium because of the current owner. He says that the buyer would probably offer somewhere in the 9's.

The house has 5 bedrooms, 7 bathrooms and a sunken family room design. It's also got a home theater, wine cellar and a massive kitchen.