Poloniex, bittrex, btc38 are biggest altcoin exchanges. You can trade/invest altcoins there, good luck.
btc38 
Haven't heard of this one.Is there any evidence that they are okay to use and invest? If less than a year old exchange I would skeptical to use them due to the recent developments with the well known exchanges.
Even if its operating more then 2 years I will never risk my bitcoins by investing into it as we don't know when they will shut their doors and run away with our money.