coingecko.com website that was suggested is a nice place, but generally speaking all the information you need to know is available on the exchanges themselves. things such as a better chart, the volume, price, changes, links,... just look at that instead of Coinmarketcap.
and also you can always use google, just search for the name of the altcoin you want to find (you can add the word altcoin or cryptocurrency to your search term) and you can find their announcement topic and website if they have any.