Hi there!
Ill make it short: duo to MS's lack of support for WebRTC (http://caniuse.com/#search=webrtc) its not possible to use the multiplayer function on mobiles (speaking of Windows Phone 8.1GRD1+).
Does someone know if it (maybe magically <img src="{SMILIES_PATH}/icon_e_biggrin.gif" alt=":D" title="Very Happy">) works, when you publish your game as an application? Maybe something is setted up by VS - I have to wait a few days untill I can buy my MS dev account, so I cant try it atm :/ - could be usefull on a another feature I want to include in my game.
I know, that it'ld be possible to use ws instead (as I read on a tutorial a few days ago) - but if Construct features a built-in multiplayer plugin (which is kinda awesome through some info I got about it <img src="{SMILIES_PATH}/icon_e_biggrin.gif" alt=":D" title="Very Happy">), Ild more likly to use this one instead of a "this should work - somehow" solution. Even when Im not needing any real-time-on-screen calculation.
Regards,
Proxymity