Most stock brokerages employ analysts. See sellside analyst for details. Despite being wrong well over 50% of the time, these analysts continue to write buy, sell, hold opinions of stocks and publish financial models and...talk. And Wall Street still listens. And pays for that research in the form of commissions/trading dollars.
So when a sellside analyst sponsors a stock (or writes positively about it), that stock usually goes up. And the bigger the brokerage, the more the stock usually moves on a big recommendation.
There is a hierarchy among sellside analysts as well. Someone from Goldman will usually have dramatically more impact on a stock's price than someone from a smaller regional firm. The top dog analyst in a given stock is called The Axe or The Hammer, don't axe us why.