Running a function in a new thread

Hello, this function is making the whole program to freeze when it's working, so I would like to put it in another thread.
The problem is I don't know how to make it work in another thread because of the arguments and to return the value.
Can you help me ?

    Function SearchForFiles(ByVal RootFolder As String, ByVal FileFilter() As String) As List(Of String)
        Dim ReturnedData As New List(Of String)                            
        Dim FolderStack As New Stack(Of String)                             
        FolderStack.Push(RootFolder)                                        
        Do While FolderStack.Count > 0                                      
            Dim ThisFolder As String = FolderStack.Pop                      
            Try                                                             
                For Each SubFolder In GetDirectories(ThisFolder)            
                    FolderStack.Push(SubFolder)                             
                Next                                                        
                For Each FileExt In FileFilter                              
                    ReturnedData.AddRange(GetFiles(ThisFolder, FileExt))    
                Next                                                        
            Catch ex As Exception                                          
            End Try                                                         
        Loop                                                                
        Return ReturnedData                                                 
    End Function