I wont say that those pump and dump groups don't exist, and since crypto trading is so recent, and anyone can take part, we probably still see people getting scammed that way, but I think the effect of those groups are getting smaller and will soon disappear as the market liquidity increases. Big money investors don't need those groups, and they can move markets by themselves right now, and I think that a lot of the pump and dump we are seeing, is done by big whales. They move the market, create a hype around it, and then manage to slowly cash out as other join, because they thing a pumping is happening. All these things will decrease as soon as we have decent market makers in the exchanges, and it would be impossible for big whales, and pump groups to move the market.
Pump and Dump group really exist but the way its being run makes it shady and the group admin is always at the one that benefit the most and the strategy is simple. Its a game of population, when you have all of them into a group, they mostly use telegram where some tips are released to get people stuck to them but really its not a tip but something with adequate study, a newbie can easily predict.
After that, all the group admin need to do is to identify the a not so popular coin in an exchange site, buy as much as possible, then start wetting the appetite of your followers of the time it would be tip would be released and when that is done, the rat race begin, while the members are trying to buy forcing the price high, the admin is trying to sell while only few members benefit due to the right timing to dump, others becomes poorer.
And the uniqueness about this group is that, only the admin is allowed to post, only him knows group members, only him gives reviews by members, only him determines those who making profit or losses and finally only him can decide when to shut down the group.