First of all, you need to file a complaint with Cyber Cell of your City for data theft.
Kindly note, in India at present we don’t have proper data privacy law, therefore, It is advisable to execute a Non-Disclosure and Non-Circumvent Agreement with your employees. Also frame an Employee Handbook Policy for your venture to be signed by all are employees.
The documentation covers the legal interest of your venture for any future violation by any of your employees. Moreover, an additional undertaking signed by the employees may protect your venture’s interest in future, even after your employee leaves and join some other organization.
The above mentioned documents are technical in nature, so its advisable to take advise of a lawyer for drafting or else it may cause more damage than the benefits, it supposed to provide.