Here's what Wall Street is saying about Twitter's CEO shake-up

Twitter dropped a bombshell after Thursday's market close with its announcement that CEO Dick Costolo was stepping down.

The move sent Twitter's stock up more than 7% in after-hours trading, as investors look forward to new management reviving Twitter's user growth.

But there are still plenty of questions around the management shake-up. Replacing Costolo on an interim basis will be Twitter cofounder Jack Dorsey, whose other job is serving as CEO of payment company Square.

How Dorsey will balance the two roles and who Twitter picks for the job on a permanent basis is unclear.

Here's what some Wall Street analysts are saying:

• "They need to take a hard look at outside candidates. Someone who not only has credibility for their industry focus, in messaging and advertising, but also someone who has credibility on the technology engineering side as well, which is where Twitter has been lacking in the past." -Baird Equity Research analyst Colin Sebastian
• "They need someone who can speak the language of advertising but also someone who can speak the language of engineering." -Baird Equity Research analyst Colin Sebastian
• "I definitely don't think Jack is going to be the next person. He's a placeholder. It's going to be between Adam Bain and someone from the outside. Adam has the inside shot because of his length of time at Twitter and probably he'll be the favored choice among employees. So I would think he's the odds on favorite right now." -Eric Jackson, Ironfire Capital.

• "I thought the board was going to stick with Dick. There was probably a lot of pressure from big investors. and probably the Chris Sacca blog post had an accelerating effect on whatever concerns or discussion there might have been before." -Eric Jackson.

• "If there's been a problem it's been with how Twitter communicated it's story more than anything. Once those expectations were put forward there was a gap between what was promised and what was delivered." -Brian Wieser, Pivotal Research Group.
  

• "It's paradoxical in the sense that you have an investor base that was dissatisfied about management turnover responding positively to management turnover." -Brian Wieser.