public class MembersController : ApiController
    {
    public HttpResponseMessage GetAllMembersByIdentifiers(string[] ids) {
                using (sampleEntities entities = new sampleEntities()){
                    var numbers = entities.tblmembers
                        .Where(p => ids.Contains(p.identify)  ).ToList();

                    if (numbers != null)
                    {
                        return Request.CreateResponse(HttpStatusCode.OK, numbers);
                    }
                    else
                    {
                        return Request.CreateErrorResponse(HttpStatusCode.NotFound, "Member with id: " + ids + " not found");
                    }
                }
            }
}

98989794, //<---
4343545345

public class MembersController : ApiController
        {

        [HttpGet]
        [Route("api/Members/Find/{ids}")]
        public HttpResponseMessage FindMemebers([FromUri]string[] ids) {


     // CHECK THE ARRAY NOT EMPTY
        if(!ids.Any() || ids.All(xx=> string.isNullOrEmpty(xx)) return Request.CreateErrorResponse(HttpStatusCode.BadRequest, "empty params");

                    using (sampleEntities entities = new sampleEntities()){
                        var numbers = entities.tblmembers
                            .Where(p => ids.Contains(p.identify)  ).ToList();

                        if (numbers != null)
                        {
                            return Request.CreateResponse(HttpStatusCode.OK, numbers);
                        }
                        else
                        {
                            return Request.CreateErrorResponse(HttpStatusCode.NotFound, "Member with id: " + ids + " not found");
                        }
                    }
                }
    }

public HttpResponseMessage FindMemebers([FromUri]List<string> ids) { ...