Twitter CEO Costolo steps down, but what next for the social media firm?

What sort of boss does the flagging microblogging site need next?

Twitter CEO Dick Costolo is leaving the social media company. The decision - which was apparently Costolo's - was announced by the CEO himself late yesterday. Co-founder Jack Dorsey is to replace Costolo on an interim basis.

Costolo made his announcement on a conference call, with the decision having been under discussion since last year, amid a company-wide conversation about succession planning.

He added that he is "tremendously proud" of his six years at Twitter, and that the firm apparently has the "strongest management team [it has] ever had". He said internal and external candidates are under consideration to replace Dorsey, who is not thinking "at all" about staying in the role permanently.

Costolo's statement is interesting considering Twitter has been on a bumpy road since its IPO in November 2013.

Twitter's constantly fluctuating value rose sharply by 3.6 per cent after Costolo's announcement - the equivalent of $900m (£581m) more in worth after it transpired its CEO was leaving the helm.

But can a new CEO solve Twitter's problems with monetising itself? Nothing the current executive team has come up with seems to have made a huge difference so far.

From breaking up personal feeds with unwelcome advertising to introducing the ability to send direct messages to unfollowed users to even - within the past day - increasing direct messages from 140 characters to a massive, spam-enabling 10,000 characters, Twitter still feels as if it is thrashing around trying to find a money-spinner.

Meanwhile, abuse on Twitter is making more and more headlines, as posts have led to criminal prosecutions and panicked removals from aeroplanes.

It's perhaps sad that one of Costolo's greatest legacies at Twitter will be his admittance that, speaking on behalf of the entire company, "we suck" at dealing with trolls and abusers.

"We lose core user after core user by not addressing simple trolling issues that they face every day," admitted Costolo earlier this year, before promising to begin banning millions of abusive and smut-peddling accounts.

This leaves a social media site that millions are already installed into and rely heavily upon, but which is seeing a plateau in its user growth and profits as its reputation begins to precede it in terms of tempting new users, while the abused quit, often never to be replaced.

All the while, Twitter adds advertising and advertising-friendly features, with no foreseeable advantages to individual users.

While the trend of social media services being born and dying - ICQ, MSN, AOL, MySpace, Bebo to name just major casualties - Twitter could learn from Facebook as it endeavours to move forward.

While Mark Zuckerberg's empire still has its ongoing problems, it's in a constant state of growth, and such moves as acquiring virtual reality firm Oculus are helping to reposition Facebook as a multi-armed IT giant, not just a friend feed.

Twitter will perhaps need a new CEO who is focused on expansion beyond the obvious. Someone with a desire to redefine - or more closely define - what Twitter actually is and represents, and how it can take its tradition of short, sharp public address and conversation to interesting new places.

The demand is still very much there for what Twitter offers, but if it becomes a lumpen sack of advertising, spam and bullying, too many people could walk away before it hits a new stride in an increasingly unforgiving digital landscape.