Kalvin Savanh grew up in Portland, Ore., and, during high school, he said, he grew marijuana. About 15 years later, Mr. Savanh, 33, still helps grow it — but now it is legal.

On Friday, Mr. Savanh and a childhood friend, William Serafica, the co-founders of Dynamiq Lightning, a Portland-based company that sells products for indoor cannabis cultivation, met near Wall Street with about 40 potential investors to encourage them to enter the cannabis industry at a time when 19 states have legalized the use of marijuana for medical purposes.

The two were among representatives from 18 start-up companies who attended a conference organized by the ArcView Investor Network, a group of entrepreneurs looking to invest in legal cannabis companies. The companies represented do not grow or sell marijuana, but rather provide services to the industry — like security, lighting and storage.