I have read several questions on here regarding this topic but my situation is slightly unique.
I have a TV mount that is about 20" wide. The studs in my wall are 24" apart. I am mounting a 55" tv. The tv weighs 53 lbs and the mount is at most 20 lbs. The mount does swivel so it might be pulled on to swivel the tv.
The way I see it I have 2 options. First, put a piece of 3/4" ply wood into the studs and mount the tv on the ply wood. Or the second is a little easier, I can mount the TV into 1 stud and use heavy duty anchors on the other side of the mount. The anchors I have say they will hold up to 110 lbs. So 2 screws into the anchors and 2 screws into the stud. It seems like this will work, but I don't want to take chances with the TV.
EDIT*** It is a steel stud. So I bought drywall toggles rated to 110 lbs. I am going to propose the following and ask what people think. There are 8 holes in the mount. What if I use the drywall toggles to mount the TV in the 2 holes nearest the center of the mount, then use Drywall anchors with a high weight rating in the other 6 holes. Between 8 anchors/toggles totaling almost 900 lbs with 2 of them mounted into a steel beam seems to me that it would be sufficient. I'd also comment that I have no intention of using the swivel feature.