Banks jittery after shaky start to Facebook IPO Bill Gross, co-chief investment officer at bond giant Pimco, added cold water to the Facebook frenzy, writing on Twitter: "I know a bubble when I see one." Meanwhile, Brian Wieser, an analyst at Pivotal Research Group in New York, told The Sunday Telegraph that Facebook's shares were implausibly priced for "perfection" as he cautioned clients against buying shares in the company. The "sell" recommendation to investors will make Facebook's advisers even more nervous ahead of the resumption of trading on New York's Nasdaq exchange on Monday morning. Despite amassing more than 900m users and tripling its profits to $1bn over the last three years, Facebook faces the challenge of squeezing more advertising from the site without angering the users that are its chief asset.