The Los Angeles company known for its Snapchat messaging app generated the largest initial public offering in Southern California history on Wednesday, raising at least $3.4 billion while valuing the firm at $23.8 billion. Snap Inc.’s IPO is the most lucrative in the U.S. since online shopping company Alibaba raised $22 billion in 2014 and the biggest for a tech company since Facebook’s $16-billion haul in 2012.