I would mount a larger 3/4-inch board up first using MOLLY BOLTS or drilling into the edges where inside wall supports might possible be. Then you can drill into the wood section to mount your heavy item using regular wood screws..
Something like this
The purpose of adding the large wood section first is to spread out the weight so that the mounts won't pull the screws out from the thin walls. You can paint the added large wood section to match your room decor...
I thought this smaller board that is just wide enough to fit the TV MOUNT was a good idea as well. As long as you can tie the back board into some strong is all you need to do...
Some of the TV areas have a solid wall behind the this panel and usualy have a sticker like this on the outside showing where the beefed up wall is located.
just my thoughts