Jonathan Vanian / CNBC:Pinterest reports Q3 revenue up 17% YoY to $1.05B, MAUs up 12% to 600M, vs. 590M est., but forecasts Q4 revenue below est.; PINS drops 13%+ after hours — Pinterest shares tanked as much as 15% on Tuesday after the company reported third-quarter financial results that missed on earnings per share and provided weak guidance.