So, to summarize, four basic solutions here.
1. Make use of transponders/ADS-B/Flarm. Both Flarm and a Mode-S transponder (with 'enhanced' surveillance) will emit a signal that contains your GPS position. This is picked up by ground stations and submitted to a central server at FR24. From there you can draw tracks and whatnot. This will only work if you have such a transponder/Flarm and there are sufficient ground stations nearby.
If necessary, the hardware to setup a transponder receiver yourself is 15 euros incl. P&P from China - all you need is an antenna and A/D converter to capture the right frequency, plus some (free) software. But you do need an "enhanced" surveillance transponder. Any Mode-S transponder can emit the signal, but getting the GPS position out of your GPS unit and into the transponder is a major certification hurdle, in case of certified aircraft.
2. Use a tracking app (such as Find My Friends) that runs on your smartphone, captures the GPS signal and sends it via a data connection (GPRS, UMTS, 3/4G, whatever) to a central server. This will only work if you have a data connection while flying. Which is generally an issue if you fly higher than about 3000 feet.
3. Use SPOT or another satellite based system. This is completely independent of the cellphone network: A SPOT tracker will directly send your position to a satellite, which will forward it to an internet-connected server. It's up to you to decide what that server should do with that position - I met a guy who was hiking in Iceland who set things up so that his position would show up on Facebook immediately.
4. Use a tracking device in the aircraft, and publish it after the flight. Almost any standalone GPS can do this, and there are tons of tracking applications for smartphones that can do this too. The functionality is also incorporated in SkyDemon, RocketRoute, Air Nav Pro, EasyVFR and so forth. But it's not "live" and cannot be used for SAR purposes.