How do I teach problem solving and logical thinking to students of age group 12-18yrs through online session I am currently researching some good content/problems to teach my students. I am referring to Mensa's Book on Logical thinking, which has a good amount of puzzles for all age groups. Is there any other site I should refer to? And what are your suggestions on teaching methodology through online session?
I would go back through old copies of GAMES magazine (libraries may have a stash somewhere).  They go the whole way back to something like 1977 and generally have lots of puzzles of various levels.  Apparently they merged together with another company back a couple of years ago.

https://gamesmagazine-online.com/product/vintage-games-packs/

In particular, I'm thinking of some puzzles where you are given a bunch of statements about a group of people and then have to derive all the information about them from logical inferences.  Generally, you'd have to lay out a diagram of some form and use that to either associate or block particular combinations until you figured everything out (much like sudoku but with logical constructions of words--this stuff predated sudoku by a long way).

As the teacher, you can "run the diagram" while the students can try to discuss the various implications of the statements.

Good luck.

(Edit: I just remembered a book I had a long time ago called "Puzzles for Pleasure" by E. R. Emmet--also a good source).