"He cleared out his apartment," about three weeks ago, neighbor Mark Clough tells PEOPLE. "It started off as a garage sale, and eventually, he put everything out in front of the apartment, like he was giving it away."
Koenig has been missing since Feb. 16, when his parents, Walter Koenig and Judy Levitt Koenig, got a note from the star. Police say there has been no activity on Koenig's cell phone and ATM card since that date, but they have received "a substantial amount of tips and information" about him.
Back in L.A., Koenig's landlord, who declined to give his name, confirmed that Koenig gave notice and paid his final rent bill last month before vacating the apartment he'd lived in for nine years.
Clough recalls that during Koenig's garage sale, "I said, 'Are you moving?' He said he was heading to Canada to stay with some friends."
With additional reporting by LESLEY MESSER and RACHEL GRICE