Bynes has recently been in the spotlight following a string of alleged traffic offences and yesterday pleaded not guilty to two counts of driving with a suspended licence.
Garth, who previously worked with Bynes on the show What I Like About You, has now told Us Weekly that she tried to offer the young star her support.
"I tried reaching out to her and I haven't been able to reach her," Garth said.
"My heart feels for whatever she is going through, and I love her dearly."
Lindsay Lohan's mother Dina recently offered advice for Bynes's parents, saying: "Just be around."