According to the coinmarketcap for the last 24h, Steem has a trading volume more than 442 million $. It is true that coinmarketcap summarize the trading volume of all exchanges and You may say that in one given exchange the volume is small and it can be manipulated. I agree on that but by my experience the pump and dump groups prefer to manipulate the price in order to get a profit 10 - 20 %. Given the all over trade volume of Steem you need a big amount of money in order to create incentives to push the price up.
In every case I agree that a big player can manipulate the price even on this volumes but I think is not the case on this pump and dump groups.