Fred Silverman gave his idea of mystery-solving teenagers to William Hanna and Joseph Barbera, founders of the animation studio named after them.
From Los Angeles Magazine:
"Hanna and Barbera met while working on Tom and Jerry cartoon shorts at Metro-Goldwyn-Mayer in the 1930s, and they started their own studio in 1957. Besides the incredible genius of the animators themselves, the secret sauce at Hanna-Barbera was the ability to churn out programming on the cheap (the fledgling outfit didn’t have the budgets that MGM did). They used new technology to copy cels and a technique called 'limited animation' that only animated parts of the image like the mouth and eyes. The Hanna-Barbera style simplified characters and backgrounds (which were inspired by their California surroundings) and created animation that was cheaper, easier to produce, and more distinctive."1
According to Scooby-Doo animator Iwao Takamoto, Joseph Barbera came up with the idea of adding a dog to the Fred Silverman's mystery show "because it had helped liven up other shows he [Barbara] had created."2
Information Sources:
1Nichols, C. (2016, November 8). Your Favorite Vintage Saturday Morning Cartoons Are Now in a Museum. Los Angeles Magazine. Retrieved from http://www.lamag.com/askchris/favorite-vintage-saturday-morning-cartoons-now-museum/
2Nelson, V.J. (2007, January 10). Iwao Takamoto, 81; animator for Hanna-Barbera drew Scooby-Doo. Los Angeles Times. Retrieved from http://articles.latimes.com/2007/jan/10/local/me-takamoto10