SAN FRANCISCO, Nov. 8 — When Seth J. Sternberg and two colleagues started Meebo, a Web-based instant-messaging service, they didn’t go looking for venture capitalists. Using their credit cards, they financed the company themselves to the tune of $2,000 apiece. It was enough to cover their biggest expense — leasing a few computer servers at $120 a month each. Within a month of its introduction in September 2005, Meebo was getting as many as 50,000 log-ins a day, and it needed more servers. It decided to take a modest $100,000 from three angel investors, wealthy individuals who typically contribute small amounts but do not get involved in management decisions.