In a touching tweet, he begged God to give him Iris back, or if not to "take extra special care of her", adding: "I love her so so much."
Iris Goldsmith was killed in an apparent quad bike accident at the family farm near the village of North Brewham in Somerset on Monday.
The teenager reportedly became trapped when the vehicle she was riding overturned, and the incident is not being treated as suspicious.
Iris was the eldest of three children born to Mr Goldsmith and his ex-wife, banking heiress Kate Rothschild, who are said to be "united in grief".
The former couple - who have two sons, Frank, 13, and Isaac, 11 - are worth hundreds of millions of pounds and hail from two of the most powerful families in the UK.
Posting a picture of his daughter on Twitter, Mr Goldsmith, the younger brother of Conservative MP Zac Goldsmith and journalist Jemima Khan, wrote: "Dear God, please can I have my beautiful, brilliant, kind little girl back, please God.
"And if not, please take extra special care of her. I love her so so much and I'm so proud of her.
"It hurts me so much I can't describe."
Iris attended Wycombe Abbey, an independent girls' boarding school in High Wycombe, Buckinghamshire, and died at the start of the summer holidays.
Headmistress Rhiannon Wilkinson said: "We were all shocked to learn from the family of Iris's tragic death. We extend our deepest sympathies to her parents and family at this sad, sad time."
Ms Wilkinson added that Iris was a "much valued and loved member of our school community" and "highly regarded in her House and year group".
A spokeswoman for Avon and Somerset Police said: "We were called at about 3.15pm on Monday July 8 to a farm in the North Brewham area following the sudden death of a teenage girl.
"The girl's death is not being treated as suspicious and officers are now carrying out inquiries on behalf of the coroner."