Twilio Inc. raised more than it expected in its initial public offering, an optimistic sign for the dozens of other technology companies that have been valued at more than $1 billion in private fundraising.

The San Francisco company's IPO priced at $15 each, raising $150 million by selling 10 million shares, the company said in a release late Wednesday. The offering comes during a tough patch for younger, private technology companies as some of their valuations in private fundraising rounds have fallen in recent months....