How to hang a TV on a drywall with no studs and no room for toggle bolts?
As Joe points out, if this wall is original, then it's not drywall, but plaster. You can't easily detect studs behind plaster walls with a stud detector. You likely have to use test holes. One option is to drill a largish hole in the center(ish) of where you will mount the TV. Then use a coat hanger to fish it into the hole to see if you can locate the studs on each side. 

If it's a solid wall (brick, likely) then that gets trickier, Old brick and mortar isn't that strong in terms of ability to hold screws. But you can try it by drilling into the mortar and using masonry screws. 

Finally, if this is a shared wall with the neighbor, first check your tenant agreement to see if you are even allowed to mount a TV to it. Lots of apartments will have restrictions on what you can hang on shared walls--both for fire code issues (they don't like holes in party walls) but also for common courtesy of trying to avoid noise transference.