SVB Financial Group SIVB, the parent of Silicon Valley Bank, saw its stock tumble more than 66% in premarket trade Friday, in a continued response to reports late Thursday that several funds were advising clients to pull their money, sparking fears of a run on the bank. Bloomberg News late Thursday reported that Founders Fund, the San Francisco-based venture-capital fund co-founded by Peter Thiel, has advised companies to do just so. The report cited people familiar with the matter.