No invaders?!

Visit friends and perform the usual three 'actions'. That way they know for sure you've been there. Then use one nerd per building attack up to five. Again they see your name as attacker. Accept that your attack will be thwarted but they earn gold out of five buildings. If they are good neighbours they should reciprocate. You repel their attack and get more gold. Simples.
The problem is a lot of neighbours are not attacking their neighbours because they feel the attack will not succeed. The bad news is that as each player increases their defences all attacks are likely to fail.
Unless players get with the programme we're going to struggle with gold supplies.