Twitter's biggest problem in one chart (TWTR)

Twitter announced on Thursday that Dick Costolo will step down as CEO on July 1.

Since being named CEO in 2010, Costolo's had a rough ride, constantly having to deal with rumors of management change at Twitter.

The biggest problem has been Costolo's inability to grow Twitter's user base at a faster pace. As seen in the chart below by BI Intelligence, Twitter's monthly active user growth on a year-over-year basis has been on a clear downward trend over the past three years. Although it did manage to up its monthly active users to 302 million last quarter, that was only an 18% increase from the same period of last year.

Costolo further worried investors during his last earnings call when he said, "We're off to a slow start in April," indicating even worse user growth numbers for this quarter.

BI Intelligence