Preferred strategies for collecting payment?

Hi HN. My family is owed a good sum of money from a family friend, a sum which was lent to said friend's business many years ago and still has not been repaid. The debtor has the money, but keeps stonewalling. It is a sensitive situation and it involves extended social networks of friends; both sides agree on the amounts, and both sides agree that it should be paid. What are some ways to, er, "incent" the gentleman in question to pay his debt, preferably not involving escalating hostilities or legal threat? Any trusted techniques for raising the temperature in a firm but civilized way? Thanks.