Facebook Inc. said Thursday it has begun testing a system for users to send messages to people outside their immediate circle of social contacts for a payment of $1, as the company continues to find new ways to capitalize on its popularity.

In a statement posted online, the Menlo Park, Calif.-based social site cited research showing that "imposing a financial cost on the sender may be the most effective way to discourage unwanted messages and facilitate delivery of messages that are relevant and useful."

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