Call a pro is never a bad idea....
(I do this for a living)
Is it an articulating mount or just flat / tilt mount?
Articulating mount with a heavy tv, you probably should hit a stud. Otherwise toggles generally work well if you can't find a stud. Most of the weight is vertical on a flat or tilt mount and most of the newer tv's are relatively light weight.
Back in good old days with 160 lbs plasma and an articulating mount .... fun fun fun, don't miss it at all.