You’ll need to register on https://developer.twitter.com and get the following details in order to be able to call the API:
Twitter_Access_Token
Twitter_Access_Secret
Twitter_API_Key
Twitter_API_Secret

The below URL is the end-point to get the users using the Twitter API:
https://api.twitter.com/1.1/users/search.json

You can do as many iterations to fetch the users and define the page size for each iteration. So, to fetch 100 users, do 5 iterations of page size 20:

int total_res = 0;
List<TUserResult> lst = new List<TUserResult>();
for (int i = 1; i <= 5; i++)
{
	string q = Convert.ToString(query).Trim();
	//code for performing oAuth request.
	string res_url = "https://api.twitter.com/1.1/users/search.json";
	//Fetch oauth application keys from the config file...
	var oauth_token = ConfigurationManager.AppSettings["Twitter_Access_Token"];
	var oauth_token_secret = ConfigurationManager.AppSettings["Twitter_Access_Secret"];
	var oauth_consumer_key = ConfigurationManager.AppSettings["Twitter_API_Key"];
	var oauth_consumer_secret = ConfigurationManager.AppSettings["Twitter_API_Secret"];

	// oauth implementation details
	var oauth_version = "1.0";
	var oauth_signature_method = "HMAC-SHA1";

	// unique request details
	var oauth_nonce = Convert.ToBase64String(
		new ASCIIEncoding().GetBytes(DateTime.Now.Ticks.ToString()));
	var timeSpan = DateTime.UtcNow
		- new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc);
	var oauth_timestamp = Convert.ToInt64(timeSpan.TotalSeconds).ToString();


	// create oauth signature
	var baseFormat = "count={0}&include_entities={1}&lang={2}&oauth_consumer_key={3}&oauth_nonce={4}&oauth_signature_method={5}" +
					"&oauth_timestamp={6}&oauth_token={7}&oauth_version={8}&page={9}&q={10}";

	var baseString = string.Format(baseFormat,
								20.ToString(),
								"false",
								Uri.EscapeDataString("en,es,fr,de,it,pt,tr,ko,ru,ja"),
								oauth_consumer_key,
								oauth_nonce,
								oauth_signature_method,
								oauth_timestamp,
								oauth_token,
								oauth_version,
								i.ToString(),
								EscapeUriDataStringRfc3986(q)
								);

	baseString = string.Concat("GET&", Uri.EscapeDataString(res_url), "&", Uri.EscapeDataString(baseString));

	var compositeKey = string.Concat(Uri.EscapeDataString(oauth_consumer_secret),
							"&", Uri.EscapeDataString(oauth_token_secret));

	string oauth_signature;
	using (HMACSHA1 hasher = new HMACSHA1(ASCIIEncoding.ASCII.GetBytes(compositeKey)))
	{
		oauth_signature = Convert.ToBase64String(
			hasher.ComputeHash(ASCIIEncoding.ASCII.GetBytes(baseString)));
	}

	// create the request header
	var headerFormat = "OAuth oauth_nonce=\"{0}\", oauth_signature_method=\"{1}\", " +
					   "oauth_timestamp=\"{2}\", oauth_consumer_key=\"{3}\", " +
					   "oauth_token=\"{4}\", oauth_signature=\"{5}\", " +
					   "oauth_version=\"{6}\"";

	var authHeader = string.Format(headerFormat,
							Uri.EscapeDataString(oauth_nonce),
							Uri.EscapeDataString(oauth_signature_method),
							Uri.EscapeDataString(oauth_timestamp),
							Uri.EscapeDataString(oauth_consumer_key),
							Uri.EscapeDataString(oauth_token),
							Uri.EscapeDataString(oauth_signature),
							Uri.EscapeDataString(oauth_version)
					);



	ServicePointManager.Expect100Continue = false;

	// make the request
	var postBody = "count=20&include_entities=false&lang=" + Uri.EscapeDataString("en,es,fr,de,it,pt,tr,ko,ru,ja") + "&page=" + i.ToString() + "&q=" + EscapeUriDataStringRfc3986(q);
	res_url += "?" + postBody;


	//Make a WebRequest to the Twitter end-point:
	HttpWebRequest request = (HttpWebRequest)WebRequest.Create(res_url);
	ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;
	request.Headers.Add("Authorization", authHeader);
	request.Method = "GET";
	request.ContentType = "application/x-www-form-urlencoded";
	var response = (HttpWebResponse)request.GetResponse();
	var reader = new StreamReader(response.GetResponseStream());
	var objText = reader.ReadToEnd();

	try
	{
		JArray jsonDat = JArray.Parse(objText);

		//ToDo: Compare the list of Ids from each iteration for duplicates.
		//General Idea for iterating through the results in each iteration:
		for (int x = 0; x < jsonDat.Count(); x++)
		{
			TUserResult twitter = new TUserResult();
			twitter.name = jsonDat[x]["name"].ToString();
			twitter.screen_name = jsonDat[x]["screen_name"].ToString();
			twitter.description = jsonDat[x]["description"].ToString();
			twitter.image_url = jsonDat[x]["profile_image_url_https"].ToString();
			lst.Add(twitter);
		}
		
		

		total_res += jsonDat.Count();
		if (jsonDat.Count() == 0 || jsonDat.Count() < 20)
		{
			break;
		}


	}
	catch (Exception twit_error)
	{
		//Handle exceptions...
	}

}

Here is the definition for EscapeUriDataStringRfc3986 method:

internal static string EscapeUriDataStringRfc3986(string value)
{
	// Start with RFC 2396 escaping by calling the .NET method to do the work.
	// This MAY sometimes exhibit RFC 3986 behavior (according to the documentation).
	// If it does, the escaping we do that follows it will be a no-op since the
	// characters we search for to replace can't possibly exist in the string.
	StringBuilder escaped = new StringBuilder(Uri.EscapeDataString(value));

	// Upgrade the escaping to RFC 3986, if necessary.
	for (int i = 0; i < UriRfc3986CharsToEscape.Length; i++)
	{
		escaped.Replace(UriRfc3986CharsToEscape[i], Uri.HexEscape(UriRfc3986CharsToEscape[i][0]));
	}

	// Return the fully-RFC3986-escaped string.
	return escaped.ToString();
}

Below are the Twitter user details classes defined:

public class TUserResult
{
	public string name { get; set; }
	
	public string screen_name { get; set; }
	
	public string description { get; set; }
	
	public string image_url { get; set; }
	
	public string errors { get; set; }
}