The Securities and Exchange Commission has failed to examine thousands of money managers it oversees, despite adding scores of examiners and doubling spending over the last 13 years.

More than one-third of the approximately 12,200 mutual-fund companies, wealth managers and other investment advisers that come under the agency's sole purview have never had an on-site check for signs of fraud or misconduct, according to data provided to The Wall Street Journal in response to public-records requests.