In Wednesday’s Analysts' Actions, Wall Street firms weigh in on Amazon (AMZN), Twitter (TWTR), and Yelp (YELP). Analysts at Stifel Nicolaus are turning bullish on Amazon, upgrading the stock to BUY from HOLD with a $700 price target saying it emerged from its investment cycle as a 'bigger, stronger, faster' company. Stifel analysts called its latest earnings 'game-changing.' Analysts at Deutsche Bank lowered their price target to $50 from $60 on shares of Twitter, following its earnings release and disappointing user growth numbers. The firm maintained its BUY rating on the micro-blogging site. And Brean Capital analysts lowered their price target on shares of Yelp to $40 from $58. The firm kept BUY rating. Brean pointed to the online review site's 'increasing number of challenges' but still sees value with takeover potential. TheStreet's Kurumi Fukushima reports in New York.