touchstone in momentum ADS

Yes..
Look at "Data Items" in component palette..

Data item is active just in the schematic environment but not in momentum.

What you wanna do ? Can you explain more detailed ?

I have a stripline circuit but in some stages have imported some components (S2P from HFSS) to the circuit. now I want to simulate it in full wave (momentum).

Simulate your microstripline only in Momentum by putting proper ports ( input output etc..) then transfer your MS line into schematic window by creating component option then connect the other stuffs in this schematic testbench and simulate them all in a single environment.