Around 60 uninvited youths with a "pack mindset" converged on Shaun Beverley's £1.1 million home, which won The Daily Telegraph Homebuilding Award in 2009, after being alerted by messages on the social networking website.
When Mr Beverley, 45, attempted to usher them off the property, a gang turned on him, punching him to the floor in a "vicious and horrendous" attack.
The architect was kicked, spat at and had objects thrown at him as he lay on the ground, Blackpool magistrates' court heard.
Yesterday, a 16-year-old boy admitted assaulting Mr Beverley at the converted 1970s bungalow, in a private road in Lytham St Annes, Lancs, on July 7 this year. The court was told that the youth, who lives in a seven-bedroom house in the same town, threw three punches before others joined in the attack.
District Judge Jeff Brailsford heard that the group conned their way into Mr Beverley's property, which has electric gates, by giving a false identity over the intercom. The judge told the teenager, who cannot be named: "You were part of a pack mindset which led to this man suffering a vicious and horrendous attack trying to defend his home and his garden in an entirely proper manner.
"He had opened up his home for his daughter's party and these people wangled their way in. They were all at least two or three years older than the girl.
"But when asked, they were not for leaving. Mr Beverley started to usher them out when he was punched to the floor by you. You became the front man and others egged you on. You are an intelligent young man and you behaved in an appalling manner. You will forever regret what you did to this man."
Brett Chappell, defending, said the boy apologised unreservedly for what he did.
"He wants to go into the Army. When he was shown the photographs of the injuries suffered by an innocent man he was totally ashamed and accepts he was a catalyst for what happened."
The youth was given a nine-month referral order during which he may have to meet his victim face to face. He must pay Mr Beverley £150 compensation and £50 court costs.
The case was the latest in a series of examples of parties turning violent after being advertised online.