New Delhi (CNN Business) The head of India's biggest coffee chain has gone missing.

Coffee Day Enterprises, the company that owns the Café Coffee Day chain, said on Tuesday that its chairman, V.G. Siddhartha, had "not been reachable" since the previous evening.

Indian police believe Siddhartha left the southern Indian city of Bangalore on Monday and traveled by car to Mangalore in Karnataka state, Mangalore police commissioner Sandeep Patil told CNN Business.

Patil said police believe the executive left his car to walk on a bridge over the Netravati river, near where it flows into the Arabian Sea. The coast guard and local fishermen were searching the river, he added.

Police at the Netravati river in Mangalore, southern India, as search teams look for Indian coffee tycoon V.G. Siddhartha.

Siddhartha founded Coffee Day in 1993 , and opened the first Café Coffee Day in the southern Indian city of Bangalore three years later. The company has since grown into India's biggest coffee chain, with over 1,700 outlets across 245 Indian cities as of last year.

Starbucks SBUX Global rival, in comparison, currently has 146 outlets in India.

Shares in Coffee Day Enterprises plunged 20% to a record low on the Bombay Stock Exchange on Tuesday following the news of its founder's unexplained disappearance.

"We are shocked by this development and our thoughts and prayers are in support of his family and loved ones," the company said in a later statement after an emergency meeting of its board.

Coffee Day included in its statement the copy of a letter purportedly written and signed by Siddhartha in which the coffee tycoon said he was facing "tremendous pressure" from lenders that led to him "succumbing to the situation." It was dated July 27.

"I would like to say I gave it my all," the letter says. "I am very sorry to let down all the people that put their trust in me."

In the letter, Siddhartha urged Coffee Day to continue running the business with new management.

"I am solely responsible for all mistakes. Every financial transaction is my responsibility," he wrote.

Siddhartha owns 33% of Coffee Day Enterprises, according to a stock exchange filing last month, while his wife and family-owned entities hold another 21%. The company went public in 2015.

Coffee Day also has retail outlets in Austria, the Czech Republic, Egypt, Malaysia and Nepal, and exports coffee to several markets including North America, Europe and the Middle East.

In the letter, Siddhartha listed the coffee chain as well as several other assets — including stakes in multiple tech companies and logistics firm Sical — that he said "can help repay everybody."

"My intention was never to cheat or mislead anybody, I have failed as an entrepreneur," he added. "I hope someday you will understand, forgive and pardon me."