REST API returning NotFound (404) if record is not found in the database

Question

I'm not really sure what the preferred way is to deal with records not found in the database. Is it better to write a Find method which returns null or a Get method which raises a RecordNotFoundException?

[AuthenticateFilter(UsernameAndSecretKey)]
[Route("api/v1/activities/emails/{id}")]
[HttpGet]
public IHttpActionResult GetEmailActivity(int id)
{
  try
  {
    // business logic service, could use only db service but this way we can do unit tests (just fill bl service method with fake objects)
    var service = new EmailActivityBlService();

    // 1. use Find method which returns null in case record with provided id does not exist in db
    var model = service.FindActivity(id);
    if( model != null )
      return Ok(model);
    return NotFound();  

   // 2. or is this approach better
   // throws RecordNotFoundException in case row by id is not found in database
   return Ok(service.GetActivity(id));
  }
  catch(RecordNotFoundException e) { return NotFound(); }
  catch(Exception e) { return InternalServerError(e); }
}

EmailActivityBlService has next code in case anyone interested (showing only the important part):

private EmailActivityDbService _dbService;

public EmailActivityModel GetActivity(int id)
{
  var model = this._dbService.GetActivity(id);
  if( model == null )
    throw new RecordNotFoundException(); // I suppose System.Data.ObjectNotFound is also suitable
  return model;
}

public EmailActivityModel FindActivity(int id)
{
  // typical entity framework query
  // using(var context = new ..) { return contect.EmailActivity.Where()..SingleOrDefault().ConvertToModel();
  return this._dbService.GetActivity(id);
}