The fastest companies to reach a $1bn valuation

Fastest launch-to-$1B valuation YouTube $1.65B 20 months Groupon $1.35B 17 months Slack $1.12B 14 months http://t.co/vAB2xGtJhY
— Doug MacMillan (@dmac1) October 31, 2014

& also

@markstrefford Good call! Instagram $1B 18 months
— Doug MacMillan (@dmac1) October 31, 2014

Note - Doug MacMillan is a tech reporter for WSJ