Mr Siddhartha has gone missing from near a river in Mangaluru in Karnataka, the police said.

He was last seen on a bridge over the Netravati river in the coastal town, according to reports.

The police have launched a massive search operation near the one-kilometre-long bridge; divers are scanning the muddy river. Cops on inflatable boats have joined the search.

In a letter that Mr Siddhartha reportedly wrote to the management and employees of the coffee chain, he expressed unhappiness over not creating "the right profitable business".

"...I have failed to create the right profitable business model despite my best efforts... Every financial transaction is my responsibility... The law should hold me and only me accountable," he wrote, according to news agency ANI.

Mr Siddhartha was recently in the news after he sold about 20 per cent of his stake in tech company Mindtree to engineering and construction company Larsen & Toubro. He was also in talks with Coca-Cola Co to sell his flagship chain to the snack food and cola giant, according to media.

Mr Siddhartha's offices were raided by income tax officers in September 2017.

He is among the country's largest exporters of coffee bean. His family has been in the coffee-growing business for more than 130 years, according to his profile page on the website of consultancy firm Mindtree, where he is a non-executive director.

Mr Siddhartha owns a 32.75 per cent stake in Coffee Day Enterprises, the owner of cafe chain Cafe Coffee Day, and is also one of the promoters of SICAL Logistics, an integrated logistics solutions provider, according to information available on the BSE.