Mostert used his Instagram account to thank The Faithful for his six seasons in the Bay Area and say goodbye.
"Man I don't even know where to begin," wrote Mostert. "To the Faithful, you guys gave me hope - a purpose to become the best player I can be. We've rode the wave together through both good times and bad. From having my first ever recorded TD against the Raiders to breaking my forearm the following series. To having my record-breaking performance in the NFC Championship game to playing in the Super Bowl and scoring a TD on the biggest stage, but unfortunately coming up short.
"I came in as a kid with a dream and left as your starting running back, team captain, and with memories on and off the field I'll never forget. My family and I have loved the past 6 years in the Bay. From the bottom of my heart, I can't thank you enough."
San Francisco signed Mostert on November 28, 2016. He rushed for 1,610 yards and 11 touchdowns on 284 carries with the 49ers while adding 36 receptions for 361 yards.
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