spark at the electrodes can be difficult to see.. it's a faint blue. Clamp the metal base of the plug to a clean spot on the engine fins and crank the engine..
ok .. did that.. no spark with the brand new plug..
you say someone may have been working on it and quit?
Do a visual check of the magneto/flywheel. Does it look like it contains all the parts? got a set of points in there? coils of wire? Find a condenser anywhere? See any disconnected wires laying around?
Is the plug lead secure in the ignition coil or did someone try to 'unscrew" something that probably doesn't unscrew...
Was the bike rewired? Do all the kill or ignition switch wires show continuty to ground with ignition on and kill-switch off (run)?
Spend some time examining the basics.. look for clues of possible tampering.
Electrically, small 2 or 4 strokes are identical.. slight variations exist between different models and brands of each, but the same basic magneto system is used.
Major electrical component failure is rare and that possibility should be at the bottom of the check list. However, in this case i have a feeling the previous owner had a no-spark problem and may have done anything.. and some things, like persistant attempts to get a spark with an ungrounded plug can damage things.
to be continued..