Take the S-bahn to Lochau-Hörbranz. Head across the roundabout to Bahnhofstraße and walk up until you come to a busier road, Landstraße, with a post office. Turn left and you will be walking towards. Cross over the autobahn and after 20m on the left there is road with several petrol stations servicing trucks. In Austria petrol is much cheaper in comparison to all neighbouring countries so these stations just before/after the border are very busy. You will find trucks going in all directions.
In fact any of the bus stops along Landstraße looked very good for catching the area traffic from Bregenz to the North but a rather general DE sign didn't work for us. After we got to the Shell station mentioned above, drivers advised us to go down on the opposite side of the road to another station where there are even more trucks! Most in that moment were going to Italy but the fifth one worked for our desired direction of Memmingen. Speaking an Eastern European language might be an advantage as drivers become much more relaxed and friendlier! We even received a coffee! June 2019, Nikola and Hannah.
South towards Feldkirch
It's hard to get on A14 from the Kennelbacherstraße, which has access to A14. There is a bus stop, but cars are going downhill and it is tough for them to stop. If you choose this spot, you should have a sign.