MAKE A CALL TO THIS COMPANY.
first, assuming there is no 'punch holes' in the stock certificate (meaning it has been cancelled and is worthless), look up the name on yahoo finance. if it is not on yahoo finance, then go to yahoo and do a general search on the name of the company on the certificate. call the 1-800 number (usually investor department) and start asking them.
If the stock is not registered in your name, or that of a close relative, it is of no value to you.
As others have told you, check Yahoo finance, or the site of some of the market places.
Calling the company is a waste of time
The best way is to call the investor relations department of the company. From that, take a photo of the stock certificate and send it to them. They might have a ton of old dividends sitting in a bank because they did not have an address to pay on.
Start with the stock market listings. The company might be listed in one of them. The Wall Street Journal lists all the major stock markets each work day. And you can probably find them online as well.
Just went online to verify my last statement. Here's the NYSE URL: [ Nyse.com Link ] You can see if your company is listed. NASDAQ also has a listing online. And I suspect AMEX has as well.
Look it up in Yahoo Finance