Forfeit Security Deposit timeframe?

[Shawn M.]

At what point is the security deposit forfeited? I have asked the previous tenants multiple times for their contact info for where to mail or wire the money and they haven't gotten back to me. I have 30 days to return the deposit as the landlord. At what point can I say sorry I'm keeping it? I dont want them to come out of the woodwork next year looking for money