csomStart2010SiteWorkflow.cs

using Microsoft.SharePoint.Client;
using Microsoft.SharePoint.Client.Workflow;
using Microsoft.SharePoint.Client.WorkflowServices;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security;

namespace CSOMWorkflow
{
    class Program
    {
        static void Main(string[] args)
        {
            //Replace the following values according to your configuration.
 
            //Site details
            string siteUrl = "https://mytenant.sharepoint.com/sites/test";
            string userName = "user@mytenant.onmicrosoft.com";
            string password = "password";

            //Name of the SharePoint 2010 Workflow to start.
            string workflowName = "SP2010SiteWF";
            
            using (ClientContext clientContext = new ClientContext(siteUrl))
            {
                SecureString securePassword = new SecureString();

                foreach (char c in password.ToCharArray()) securePassword.AppendChar(c);

                clientContext.Credentials = new SharePointOnlineCredentials(userName, securePassword);

                Web web = clientContext.Web;

                //Workflow Services Manager which will handle all the workflow interaction.
                WorkflowServicesManager wfServicesManager = new WorkflowServicesManager(clientContext, web);
				
		//Will return all Workflow Associations which are running on the SharePoint 2010 Engine
                WorkflowAssociationCollection wfAssociations = web.WorkflowAssociations;
				
		//Get the required Workflow Association
                WorkflowAssociation wfAssociation = wfAssociations.GetByName(workflowName);

                clientContext.Load(wfAssociation);

                clientContext.ExecuteQuery();
				
		//Get the instance of the Interop Service which will be used to create an instance of the Workflow
                InteropService workflowInteropService = wfServicesManager.GetWorkflowInteropService();

                var initiationData = new Dictionary<string, object>();
				
		//Start the Workflow
                ClientResult<Guid> resultGuid = workflowInteropService.StartWorkflow(wfAssociation.Name, new Guid(), Guid.Empty, Guid.Empty, initiationData);

                clientContext.ExecuteQuery(); 
            }
        }
    }
}