Snapchat, a rapidly growing messaging service, recently spurned an all-cash acquisition offer from Facebook for $3 billion or more, according to people briefed on the matter. The offer, and rebuff, came as Snapchat is being wooed by other investors and potential acquirers. Chinese e-commerce giant Tencent Holdings had offered to lead an investment that would value two-year-old Snapchat at $4 billion.