In many ways, Joshua Bryce Newman fits the part of the young, successful entrepreneur.

A 35-year-old Yale graduate, Mr. Newman began investing in Internet start-ups during his junior year. After college, he ran an independent movie production company in New York and helped found two popular CrossFit gyms in Manhattan. His website cites several news articles that describe him as “a Silicon Valley pro” and “an Internet elder statesman,” and as being “sharp and supremely confident.”

But some of the nearly two dozen people who have either invested with Mr. Newman or lent him money over the last decade paint a less favorable picture. In lawsuits that have been filed against Mr. Newman or companies he controls, investors say that he has a history of bouncing checks, unpaid debts and misrepresented intentions.

While the total amount in dispute appears to be relatively small — roughly a few million dollars — the way Mr. Newman has managed to raise money easily from sophisticated businessmen, many with a track record of investing in Internet start-ups, is a vivid reminder of how the right connections and a strong sales pitch can seduce investors, even after the financial crisis.

The investors include a co-founder of a social messaging site that was acquired by Google and a founder of an online apparel company. They were typically introduced to Mr. Newman at a Yale event, in a casual meeting at the Sundance Film Festival in Utah or on the recommendation of someone in the close-knit community of so-called angel investors in technology start-ups.