You need to pass the Interface Identifier (IID), so something like this:

point_container->FindConnectionPoint(IID__ISTIEventsEvents ,&conn_point);

If you don't have defined in a header file, you can create it using the #import "mytlb.tlb" directive, or just create it manually anywhere in your code using the 192B9F3E-DF39-41A5-95E0-0333B061CAB8 value.