Find a list of things that have a given member set to a given value: –

List<Thing> foundThings = listOfThings.FindAll(x => x.member == searchParam);
if(foundThings.Count == 0)
    return false;

// Do something with the foundThings

Find a single thing that matches a given criteria: –

 Thing thing = listOfThings.Find(x => x.member == searchParam);
 if (thing == null)
   return false;

// Do something with the thing