The top manager in a company is likely to be its director, president or chief executive officer; that person's details are usually published by the company as part of its legal obligation to provide information. However, this can be by name only, so obtaining contact details can be more difficult.
While there is no single register of companies' top personnel held in the United States, many companies file this information along with their required documentation to the Electronic Data Gathering, Analysis and Retrieval system held by the U.S. Securities and Exchange Commission. It is also frequently added to credit records to help reassure investors, so the records held by credit companies can help.
If the state in which the company is registered is known, local authorities often hold a record of companies that includes information about key people. The advantage of this is that state government websites are more likely to provide a search tool for people looking to find particular companies, making searches easier.
Modern social networking tools such as LinkedIn can also help, if the company or the person in question has created an up-to-date profile. The advantage of these methods is that contact details are more likely to be available if such an entry exists.