This is one example how you could use a relay for signal switching in loopers. The relay type should be suitable for audio applications. The schematic shows the relay in the non-powered state (FX-bypass). Connect your guitar to the signal input, your amp to the signal output, FX send to your effect input and FX return to your effect output. If you want more than one loop, put several of these relays in series.
When switching a preamp/FX out of the signal path, you should connect its input to ground and connect its output to ground via a resistor, so that zero voltage is at the output when putting it back in the signal path. Additionally, you could connect an R/C-network to the relay coil (try 47R/47uF as a start), because often the current peaks caused by the relay switching cause interferences (pops/cracks) in the signal path.