No need to panic! 24 hours is not a long time and there are various factors involved such as pitch temp,, aeration of wort, fermentation temperature, size of starter, etc. Typically if you pitch cold the yeast takes a bit to acclimate and go through the growth phase as they gear up to begin actively fermenting your beer.
If things go 72 hours and still appears nothing is happening then take a reading. You could also have a leaky seal in the bucket lid allowing the gas to escape from somewhere other than the airlock.