MUMBAI, Nov 21 (Reuters) - India's market regulator has asked for trading data on companies mentioned in a Reuters story last week about prescient messages on company earnings in social media chatrooms, a person familiar with the matter told Reuters on Tuesday.

The Reuters investigation documented at least 12 cases of prescient messages about major Indian companies being posted in WhatsApp groups limited largely to traders and market insiders.

"The regulator has asked the exchange to track the trading data for the companies mentioned in the Reuters report before and after their results were made public," said an official at one of the bourses, who asked not to be identified, as he is not authorised to publicly discuss the matter.

Earlier on Tuesday, Indian newspaper Economic Times, citing an unnamed official, reported that the regulator has asked the exchanges for this data.

Indian markets regulator the Securities and Exchange Board of India (SEBI), the National Stock Exchange and rival bourse BSE Ltd BSEL.NS all did not respond to requests for comment.

Ajay Tyagi, chairman of SEBI, told Reuters last week that the regulator will investigate the matter.

The messages about the 12 companies with prescient information obtained by Reuters involved mostly what were characterised as being upcoming quarterly results, including specific metrics such as net profits, revenues and operating margins.

They also included messages about upcoming bonus share issues or revenue guidance.

Seven of the companies are part of the benchmark NSE index .NSEI : Dr. Reddy's REDY.NS , the drug maker Cipla CIPL.NS , Axis Bank AXBK.NS , HDFC Bank HDBK.NS , Tata Steel TISC.NS , IT services firm Wipro WIPR.NS and Bajaj Finance BJFN.NS .

The other five were Mahindra Holidays and Resorts MAHH.NS , Crompton Greaves Consumer Electricals Ltd CROP.NS , IT services providers Mindtree Ltd MINT.NS and Mastek Ltd MAST.NS , and India Glycols IGLY.NS , a petrochemicals company.

India beefed up insider trading rules in early 2015, and it expanded what material constitutes "unpublished price-sensitive information" to include "any information" that is not "generally available" and that could have a market impact.

(By Abhirup Roy, editing by Euan Rocha and Jacqueline Wong) ((abhirup.roy@thomsonreuters.com; + 91 22 6180 7067; Reuters Messaging: abhirup.roy.thomsonreuters.com@reuters.net))